CE Course 3

Do You Know if Your Patients, Co-workers, Friends, Family, or You Have an Addiction?

Credit: Continuing Education Hours: 2
If you have specific questions about the CE requirements in your state, or if you're not sure if the course will be accepted, please consult your state dental board.

After reading this CE course, click this link to pay and take the test. Pay and take the CE test.

Table of Contents

Course Goals

The purpose of this course is to increase dental hygienists' knowledge of substance abuse and to articulate their role and responsibilities in the identification and treatment of individuals who are chemically dependent.

Learning Outcomes

Upon completion of this continuing education course, the learner will be able to:

  • Explain evolving attitudes towards chemical dependency
  • Identify three causes and three ways to prevent substance abuse
  • Describe the types and effects of abused substances
  • Identify intraoral and extraoral manifestations of substance abuse
  • Explain the dental hygienist's role in managing clients who are substance abusers

Assessment Method: Post-test only


Substance abuse (chemical dependence) is often a silent, but pervasive problem in today's society. Chemically dependent people come from all components of society, regardless of financial status, ethnicity, or age. They are masters at disguising their addictions.

A variety of chemicals, including over-the-counter, prescription, and street drugs are used and abused. Dopamine, a neurotransmitter in the brain, appears to be the major determinant in whether or not a person progresses from casual substance use to substance abuse. This course will discuss commonly abused types of substances, signs of substance use (psychological, physiological, oral manifestations), and the role of dopamine in the addiction process. An outline of successful interventions and preventive strategies will be included. Because health care professionals should be aware of the many aspects of substance abuse, this course is designed to increase understanding of the clinical and social aspects of the problem. It will provide information to help a patient, co-worker, or family member manage this debilitating and complicated problem.


"Although substance abuse is a major concern throughout the world, this course will only include the use and abuse of drugs in the United States.

Attitudes of people in the United States towards drug abuse changed rapidly in the beginning of the 19th century when patented medicines containing morphine and opium were often used to treat coughs, diarrhea, dysentery, and "women's pains." These opiates were the most effective methods available to physicians to relieve the pain of virtually any ailment.1
Opiates were rarely used as recreational drugs until the Civil War, when soldiers were treated with injected morphine and experienced the same euphoric effects as dancing, smoking, and gambling. People were viewed not as drug abusers but "spiritually weak."2

By the end of the 19th century, it became easier to isolate and produce morphine, cocaine, and opium. Since there were no legislative controls over these drugs, they were readily available from pharmacists and physicians and were heavily promoted by pharmaceutical firms.3
Parke-Davis offered coca and cocaine in forms that could be smoked, sniffed and injected, and Coca-Cola even created a soft drink with it. Despite questions about cocaine's safety, most medical experts considered it a harmless stimulant. Therefore, its use spread quickly across the United States and stories of overdoses, addictions, reactions, and the antisocial behavior of users began to rise. At the same time, another opioid, morphine, was made a prescription drug, and its use declined, due largely in part to the public's awareness and apprehension about addiction and the casual-use of habit forming drugs.4

The federal government passed laws early in the 20th century to control substance abuse. The Harrison Narcotic Act of 1914 limited the sale of opium, morphine, heroin, cocaine, and other drugs to small quantities, except when prescribed by a physician. Thereafter, abuse of opiates declined, except among people of middle to higher classes.4

The popularity of cocaine also dropped, except for among Hollywood celebrities and those involved in the criminal world. In the 1920s and 1930s, marijuana was brought to the United States by Mexican immigrant workers, and its use spread to jazz musicians.4

The picture began to change following World War II. New medications, such as tranquilizers and other mind-altering prescription drugs, became the substances of choice--especially since they were used for relieving anxiety and depression. At the same time, organized crime began smuggling narcotics into the United States on a larger scale.4

Between the 1960s and 1970s, drug addiction was being discussed as a symptom of psychological problems, requiring hospitalization for treatment. Marijuana was "rediscovered" by teenagers and was widely use\ by this age group and continued through the '90s. Hallucinogenic drugs, termed the "psychedelic" or "conscious-expanding" drugs such as lysergic acid diethlamide (LSD) and mescaline also became popular, as did designer drugs such as methylene dioxymethamphetamine (MDMA--an appetite suppressant), and phencyclidine (PCP--an anesthetic). Heroin, barbiturates, amphetamines, and cocaine became readily available to athletes and the wealthy.4

The 1980s and 1990s brought extensive use of crack cocaine and a subsequent increase in crime and violence. The term designer drugs was first used to describe synthetic or laboratory-produced derivatives of prescription drugs controlled by the U.S. Food and Drug Administration (FDA). Until late in 1986, as long as such drugs were not identical to controlled drugs, their producers could not be prosecuted or fined for making them. "Designer drug" also refers to a known, abused drug that has been repackaged or redesigned for easier use or increased appeal to consumers. Crack cocaine is such an example.

In addition to these newer drugs, alcohol abuse continues to be a major health risk in the United States. A recent report to the U.S. Congress estimates that 18 million adults 18 years and older are currently having problems resulting from alcohol use, many of them are actually addicted to it.5 A National Institute of Mental Health survey of more than 20,000 U.S. adults found that 13.7% had experienced problems with alcohol dependence, and that one half of those who were alcoholics had at least one additional problem, such as abuse or addiction to another drug.5 The inefficacy of intervention programs, complicating social and cultural factors, and controversies over the causes and treatments for substance abuse make this a complex issue. Therefore, health care professionals should be able to identify substance abusers, as well as be armed with adequate information to attempt to help them.5


Participants in this course may ask themselves am I aware of the silent, pervasive addictions infiltrating the United States? Could these addictions be affecting people in my office, my community, and my home? The answers may be yes because substance abusers are masters at disguising their condition. They come from all segments of society regardless of their financial status, ethnic background, or age. The following case histories may sound familiar:

Joan, a 30-year-old divorced mother of two, owned her own business. As the stress of her job increased and the demands of raising her two children alone became more difficult, she began using alcohol to cope. It started with one drink after work a couple of nights a week, but eventually, she was consuming two and three drinks after work every night. After six months of this pattern, her performance at work was declining. A co-worker noticed the changes in Joan's behavior and suggested she get help. Joan denied her addiction to alcohol until she was charged with DUI at the scene of an accident in which she hit a child on a bicycle.

Jim, a popular high school senior, was actively involved in athletics and clubs and did not appear to have any stress in his life. Unknown to others, Jim had smoked since he was 10 years old, and during his senior year of high school had started experimenting with marijuana "just for fun." Since he enjoyed marijuana, he thought some other drugs might make him feel even better, so he tried cocaine. His experience with cocaine was different, but he felt he was still in control. However, his cocaine experience led to addiction. He lost his athletic scholarship and found himself struggling to maintain his once high grades. Meanwhile, his self-esteem and popularity plummeted. Jim's parents admitted him to a substance abuse treatment facility, and he was finally able to get his addictions under control. Although it was not in time to save his athletic scholarship, it did give him a better chance at life.

This third case did not end as well. Cindy, a bright, cheerful college student, wanted to be a Certified Public Accountant (CPA) and was well on her way to a successful life. She was fun to be around, well adjusted, articulate and focused, as her parents had taught her to enjoy life. However, her life ended abruptly when, Mark, a fellow student with whom she was riding, crashed his car into another vehicle, killing both Cindy and the driver of the other car. Unknown to Cindy, Mark was under the influence of alcohol and also had been free-basing.


Defining the terms drug, substance abuse, and chemical dependence is a logical beginning. Taber's Cyclopedic Medical Dictionary defines a drug as any substance that when taken into a living organism, may modify one or more of its functions.6 Drugs are classified according to their biochemical action, physiologic effect, or the organ system(s) they affect. According to Inaba, et al., drug abuse is the continued use of a drug despite negative consequences. Chemical dependence refers to the interaction between a drug and the individual when there is a compulsion to take the drug to obtain its effects and/or to avoid the discomforts of withdrawal.7 Simply stated, if a substance is intentionally taken to alter one's mood or perception, it can be considered an "abused substance."

Regardless of their legal use status, drugs are classified in specific categories as: cannabinoids; central nervous system (CNS) stimulants (sypathomimetics); CNS depressants (anxiolytics); opiates (opioids); hallucinogens (psychedelics; inhalants; anabolic-androgenic steroids (hormones); prescription drugs; and over-the-counter (OTC) drugs. Categories of drugs with their effects, street names, signs, symptoms, and treatments for the abuse of each are shown in Figure 1.

Dopamine is the neurotransmitter of reward active in alcohol, opiate, and cocaine dependence.
Release of dopamine affects the part of the brain that regulates motor behavior. The destruction of the neurons that produce dopamine by substance abuse produces symptoms of Parkinson's disease, such as rigidity and tremor. Blockage of the actions of dopamine in other brain regions accounts for the therapeutic activities of anti-psychotic drugs. This neurotransmitter has been linked to addiction through its role as a pleasure chemical and enhancing learning and appears to be the common neurotransmitter affected by all addictive substances.

Other neurotransmitters involved in the brain reward system are:

Serotonin--Changes in the activity of serotonin producing neurons results in changes in mood, appetite, sleep, and sexual function. Medications to treat depression focus on increasing serotonin levels in the brain.

Enkephalins--These neurotransmitters are normally occurring substances that bind to localized opiate receptors, sites involved in pain perception. They mimic the effects of opiates.

Adapted from Snyder, S.H. Drugs and the Brain, Scientific American Library, New York, 1996.

Physiologic Effects

So what happens in the brain of people when they take a drug into their body? A simple review of basic brain anatomy and physiology will assist in understanding substance abuse and addiction. Although a comprehensive review of this topic is beyond the scope of this course, a list of resources is provided for those interested in further study of this aspect of addiction.

The organized layers of the brain can be thought of like floors in the house. Vital functions such as heart rate, breathing, and blood pressure are controlled by the brain stem, hind-brain, and mid-brain--the first floor.8

The central core of the brain--the second floor--is divided into two sections: the hypothalamus and the limbic system. The hypothalamus controls important biological functions such as sex drive, thirst, hunger, sleep cycle, energy level, the immune system, and "pleasure centers." The limbic system is called the "emotional brain" and plays an important role in regulating emotional behavior.8

The cortex, the third floor, is the highest level of the brain and is responsible for perception, information processing, thinking, reasoning, and higher cognitive functions. The frontal lobes of the cortex can be thought of as the penthouse. The front halves of these lobes are especially critical because they are active in inhibiting emotional reactions, maintaining attention and concentration, and enabling complex thinking and problem solving.8

The inside in the brain at the molecular level can be compared to the wooden structure of the house in that wood is made up of millions of grains. The grain in the wood is like the millions of nerve cells (neurons) that make up the brain. Normal brain function is dependent on the appropriate action of neurons. Each neuron functions by producing and releasing a particular chemical substance called a neurotransmitter. These neurotransmitters are called messenger molecules because they influence other neurons and assist in the transmission of messages from neuron to neuron. Neurotransmitters can impact the function of the nerve cell by activating and inactivating the cell and causing adjacent cells to produce and release hormones or to grow or to die.8

The neurotransmitters that have been associated with addiction include serotonin, dopamine, norepinephrine, gamma-amino-butyric acid (GABA), and glutamate. Medications, recreational drugs such as alcohol and cocaine, stress, genetic factors, and hormonal factors have been found to interfere with nerve cell function. This discussion will focus on the interaction between alcohol, drugs, neurotransmitters, the brain's pleasure center, and addiction.8

The pleasure centers of the brain are areas that are part of an internal biological reward system. They are activated by the release of particular neurotransmitters that are triggered by certain life experiences. Under normal circumstances, experiences such as watching a funny movie, enjoying a meal or making love can produce a range of feelings from joy to euphoria. Pleasure centers can also be activated artificially.8 For example, a person can temporarily feel on top of the world by drinking a glass of wine because of the release of dopamine, a neurotransmitter discovered in 1958.

The cell membrane, which directs the flow of chemicals in and out of the cells, can be altered by drugs, making it less stable and allowing more chemicals to enter. Therefore, certain chemicals, such as alcohol and cocaine can damage cell function.8

Addiction occurs when the body responds to repeated substance use by increasing its level of resistance to the immediate drug effects and tolerance is developed. While trying to maintain a normal state, the cell membrane is changing, as the receptors and brain chemicals try to help the brain function normally. Eventually, the body is unable to function in the altered state without the drug.

Research has also shown that dopamine plays a role in learning by drawing a person's attention to a particular event associated with past pleasure or reward. Dopamine is now also thought to be a stimulus for behavior…anticipating that pleasure or reward might follow.9 So as a person experiments with a chemical substance and finds it makes him feel good, they are creating a memory of pleasure. So the next time they think about drinking alcohol or using a drug, if the memory of pleasure is now present, they may continue its use. This cycle is described in Figure 2.

Research has shown that the progression to addiction usually occurs in three stages--experimental, tolerance, and dependency. In the initial stage, an individual tries a substance and it feels good. In the second stage, tolerance, an individual may progress to using the substance often, eventually needing more to achieve the original effect. Many people feel embarrassed or guilty at this point. In the third stage, dependency, an individual requires the substance daily. Physical side effects, such as loss of appetite, nutritional deficiencies, infections such as hepatitis, AIDS, and sexually transmitted diseases (since sex is often traded for drugs) are noticeable.

Signs of Substance Abuse

Because substance abusers come from all socioeconomic and cultural groups, health care professionals often encounter people who are skilled at masking their addiction and enlisting the aid of others to obtain drugs.2 Some of the more obvious physical and behavioral signs of substance abuse are:

  • Careless in appearance, dress, and personal hygiene (especially in someone who is usually neat and well-groomed)
  • Wearing long sleeves to cover needle marks
  • Dramatic weight loss
  • Wearing sunglasses to mask dilated or constricted pupils or eye redness
  • Unusual behavior such as gazing or slurred speech

Psychological and social signs include:

  • Anxiety, insomnia, depression, and suicide attempts
  • Social isolation
  • Mood changes
  • Severe marital problems and status changes
  • Social problems at work or school
  • Frequent job changes and moves to new areas
  • Changes of friends or associates
  • Child or spouse abuse

Oral Effects

Oral manifestations of substance abuse vary, but abusers tend to have a higher incidence of dental caries and periodontal disease than the general population.10 This may result from neglect more than drugs, but cocaine addicts may apply the drug to gingival tissues, and it may be directly responsible for the oral disease. Cocaine abusers may also exhibit angular cheilitis, oral candidiasis, glossodynia, cervical abrasion, gingival laceration, and severe bruxism. Patients with combined cocaine and alcohol addiction tend to exhibit the most severe oral disease conditions and symptoms, such as severe xerostomia, advanced periodontitis, many decayed teeth, many missing teeth, and severe tooth attrition from bruxism. Oral manifestations of cocaine use include reduced salivary secretions, increased dental caries, abnormal tooth-wear patterns, and acute gingival inflammatory effects.10

Individuals who are opiate-dependent may exhibit dental caries on the labial and buccal cervical one-third of the teeth rather than on the occlusal or interproximal surfaces. These lesions are usually darker, larger, and less painful than routine caries. Allergic thrombocytopenia caused by the quinine in adulterated heroin may appear as ecchymosis (an irregular formed hemorrhagic area) of the oral mucous membranes. Marijuana users tend to have a greater incidence of decayed, missing, and filled teeth, stain, and greater microbial plaque with resulting gingivitis. People who abuse alcohol also exhibit extra oral signs including breath and body odor of alcohol, hand, tongue and eyelid tremors, redness of the forehead, cheeks and nose, and jaundice of the face.10

Techniques for Aquiring Drugs

It is also important for oral health care professionals to be aware of the techniques addicts often used to obtain substances. Some of the more common are:

  • Telephone requests for analgesics
  • Complaints of anxiety, fatigue, insomnia, or depression, followed by requests for stimulants or depressants
  • Requests for premature refills for "stolen" or "lost" medication, or medication left at home while on vacation
  • Consistent failure to keep appointments, or refusal of treatment or lab work despite drug requests
  • Pressure, including the use of guilt, sympathy, or the threat of harm
  • Requests for specific controlled substances or drugs that are inappropriate for the individual's problem or procedure
  • Claims of being allergic to all drugs except certain controlled substances
  • Requests from elderly patients who, through confusion or deliberate effort, obtain multiple prescriptions for the same drug, or who are taking conflicting medications
  • Requests for extra medication from patients claiming to be going on vacation or a business trip
  • Visits to several different physicians for the same reasons
  • Theft of prescription pads

Screening for Addiction

When screening a patient for drug abuse, the oral health care professional should take a nonjudgmental approach and:

Ask specific, factual questions that do not permit yes and no answers.
Be persistent: if answers are vague, reword the question or say "I don't understand."
When patients are antagonistic or evasive, recognize this behavior as part of their denial mechanism.
Be sympathetic, letting the patient talk about the reactions of their family and friends to their use of drugs.
Don't accept qualified answers. If the response is "hardly at all," ask how often that means.
If users seem to be holding back information, contact family members for additional information about the extent of drug use.
End the interview on a less threatening topic so the patient will be comfortable in future discussions.


Drug abuse is a complex problem thought to result from a combination of hereditary, psychological, and environmental factors. It affects people from the neonatal stage to old age. Infants of abusers may suffer from neglect or the effects of parental drug use. As they grow into childhood, they may demonstrate antisocial behavior, and signs of malnutrition, poor self-esteem, depression, or attention deficit disorder. This may lead an adolescent to use drugs, have unwanted pregnancies, and drop out of school. Identification of drug abuse is a difficult first step on the road to recovery because of the methods many abuses use to hide their addiction, the inability of family members to recognize or accept the problem, and the relatives' enabling behavior.

Oral health care professionals, have an ethical responsibility to inform patients of how drug abuse can damage their health. With increased knowledge of chemical dependency, one may be able to identify and encourage a patient, co-worker, or family member to seek the support needed to change substance abuse habits. The self-assessment checklist and list of resource may provide insight and information helpful to someone who must take that difficult first step to recovery.

Self-Assessment Questions

Following are some self-assessment questions aimed at helping you decide where you are in relation to an addiction. Answer these as honestly as you can. You may wish to discuss the results with a professional experienced in dealing with addiction, an addict in a recovery program, or someone else you trust.

  1. What are the substance(s) or behavior(s) that you are concerned about possibly being addicted to? When did you start these, and how long have you been involved with them? How much, and how often, do you use the substance(s) or participate in the behavior?
  2. What is your usual pattern of engaging in this behavior (for example: every day, several times each week, several times per month), and how has it changed over the past several years (that is, is it getting worse)?
  3. How has this substance or behavior affected your physical health?
  4. How has this substance or behavior affected your thinking patterns, concentration, or attitudes?
  5. How has this substance or behavior affected your moods or feelings?
  6. How has this substance or addiction affected your behavior?
  7. How has this substance or behavior affected your personality?
  8. How has this substance or behavior affected your self-esteem?
  9. How has this substance or behavior affected your motivation and your job or school performance?
  10. How has this substance or behavior affected your financial condition?
  11. How has this substance or behavior affected your relationships with your family, including your children?
  12. How has this substance or behavior affected your relationships with friends or other people?
  13. How has this substance or behavior affected your ability to conform to the laws of society?
  14. How has this substance or behavior affected your religious beliefs and/or your spirituality?
  15. What other ways has this substance or behavior affected you?
  16. Who in your life has expressed concern over your possible addictive use of a substance or involvement in an addictive behavior? What exactly was the nature of this concern?
  17. How would your life be different if you did not use this substance or engage in this behavior?
  18. After reviewing your answers to these questions, what conclusions do you reach about yourself in terms of addiction(s)?

Adapted from: Daley, DC. Kicking Addictive Habits Once and for All. San Francisco: Jossey-Bass Publishers; 1998: 5.


Alcoholics Anonymous World Services, Inc.
PO Box 459, New York, NY 10163, (212) 870-3400,

Al-Anon Family Group Headquarters, Inc
1600 Corporate Landing Parkway, Virginia Beach, VA 23454-5617. (800) 356-9996 or (800) 356-2666

Cocaine Anonymous
6125 Washington Boule-vard, Suite 202 Los Angeles, CA 90230

Columbia Addiction and Substance Abuse Center (CASA)

PO Box 435 Ann Arbor, MI 48106,
(800) 222-5145

Marijuana Anonymous
PO Box 2912, Van Nuys, CA 91404

Moderation Management
(612) 512-1484

Narcotics Anonymous
PO Box 9999, Van Nuys, CA 91409, (818) 773-9999

National Center on Addiction and Substance Abuse
152 West 57th Street, New York, NY 10019

National Clearinghouse for Alcohol and Drug Information
PO Box 2345, Rockville, MD 20847-2345 (800) 729-6686

About the Author

Patty Bonasso Byrd, RDH, is a Professional Educator for Philips Oral Healthcare, makers of sonicare, and a Clinical Instructor in Dental Hygiene at the University of Louisville. As a graduate from the University of Louisville (1978) with 22 years in dental hygiene , she has done extensive consulting and lecturing nationwide on numerous topics in the dental industry. She has been actively involved in her Kentucky State Dental Hygienists' Association as vice-president, president-elect and president (1998-1999). She has also been a delegate for four years to the American Dental Hygienists' Association.

Supplemental Activities

  • Visit Procter & Gamble's Web site: www.dentalcare.com for additional information. Click on Research Resources, then click on Internal Medicine. At least the following are available: Hypertension, Effects of Hypertension, Congestive Heart Failure, Diabetes, and Epilepsy.
  • Visit Procter & Gamble's Web site: www.dentalcare.com for additional continuing education courses. At least the following are available under Courses for Dental Hygienists: Seizure Disorders, and Asthma (under Courses for Dentists).
  • Participate in courses offered by the American Red Cross, such as Responding to Emergencies, 'Til Help Arrives, Emergency Response, Community First Aid and Safety.
  • Order and complete: Medical History Evaluation and Management of Medical Emergencies package from Jill Stoltenberg at the University of Minnesota, Department of Preventive Sciences, Division of Dental Hygiene, Clinic Director: 612/625-5651.
  • Visit www.centerwatch.com/drugs for the most recent information about prescription drugs.

Additional Readings

  • Blum K, et al.: Reward deficiency syndrome. Amer Scientist 1996;84(2):132-145.
  • Board of Trustee Report. Drug abuse in the United States. Strategies for prevention. JAMA 1991:265(160):2102.
  • Cochran J: Substance Abuse: Drugs. Miami, Health Studies Institute, 1995, p.108-109.
  • Inaba DS, Cohen WE, Holstein ME: Uppers, Downers, All Arounders. Ashland, OR: CNS Publications, Inc. 1997.
  • Lowinson JH, Ruiz P, Millman RB, Langrod JC, eds: Substance Abuse. A Comprehensive Textbook. Baltimore, Williams & Wilkins, 1992.
  • Rees TD: Oral effects of drug abuse. Critical Reviews in Oral Biology and Medicine 1992;3(3):163-184.

Definition of Terms

Abuse—pattern of abnormal drug use that occurs despite negative consequences or the threat of physical damage; not the same as addiction.

Addiction—physical and psy-chological dependence, includ-ing tolerance of a drug, withdrawal symptoms when use is stopped, and persistent relapses following reversal of physical dependence.

Chemical dependence—a primary chronic disease with genetic, psychosocial, and environmental factors influencing its development and it manifesta-tions.

Codependency—suffering and/or dysfunction that is associ-ated with or results from focusing on the needs and behavior of others. A constellation of responses by significant others, particularly family, to being involved with the dependent.

Designer drugs—a term first used in the 1980s to describe synthetic or lab-produced derivatives of prescription drugs con-trolled by the U.S. Food and drug (FDA). Until late 1986, so long as drug imitations were only similar, but not identical, to controlled drugs, individuals could not be prosecuted or fined for making them. Designer drug can also refer to a known, abused drug that has been repackaged or redesigned for easier use or increased appeal to consumers. Crack cocaine is a designer form of cocaine.

Dependence—a condition marked by use of a substance in excessive dosages or for a longer period than directed by a physician; use despite persistent social, psychological, and physical problems; expenditure of considerable effort to obtain,use, and recover from a sub-stance; withdrawal symptoms or repeated failure to reduce or control use; and continued use to relieve or avoid withdrawal symptoms.

Drug abuse—regular use of a drug other than for its accepted medical purpose or in doses greater than those considered appropriate.

Ecchymosis—a small hemorrhagic spot, larger than a petechia, in the skin or mucous membrane forming a non-ele-vated, rounded or irregular, blue or purplish patch.

Experimental—the stage during which individuals become aware that a substance makes them feel good.

Gateway drugs—substances such as, alcohol, tobacco and marijuana, thought to lead to use of more addictive sub-stances.

Glossodynia—pain in the tongue.

Neurotransmitters—chemicals that stimulate adjacent neurons.

Physical dependence—physical adaptation to chronic use of a specific psychoactive substance. Withdrawal symptoms develop when use ceases, and may be relieved when use is resumed.

Psychological dependence— a subjective sense of need for a specific psychoactive substance, to experience its posi-tive effects or to avoid the negative effects associated with stopping its use.

Substance abuse—regular use of a drug other than for its accepted medical purpose or in doses greater than those con-sidered appropriate.

Thrombocytopenia—a decrease in the number of blood platelets.

Tolerance—the need for higher and higher doses of a drug to achieve the same effects. This occurs because of alternations in drug metabolism, so that the liver destroys the drug more quickly, and because of changes in the target cells (usually those of the nervous system).