Disorders of Reward, Drug Abuse, and their Treatment
Psychopharmacology is generally defined as the study of drugs that affect the brain. Until now, all the chapters of this book have addressed how psychotropic drugs affect the brain for therapeutic purposes. Unfortunately, psychotropic drugs can also be abused, and this has caused major public health problems throughout the world. Here we will attempt to explain how abuse of psychotropic agents affects the brain. Our approach to this problem is to discuss how nontherapeutic use, short-term abuse (intoxication), and the complications of long-term abuse affect chemical neurotransmission, particularly within reward circuits. We will also discuss the mechanism of action of agents that are now used to treat various substance abuse disorders.
Also covered briefly in this chapter are several other disorders thought to be regulated by reward circuitry, including sexual disorders, eating disorders, and various impulse disorders such as gambling. Reward circuitry has a prominent role in most psychiatric disorders, not just in drug abuse. Indeed, links to the reward circuitry can be seen not only for disorders of impulsivity such as attention deficit hyperactivity disorder (ADHD) (discussed in
TABLE 19-1 Paradigm-shifting questions for the modern treatment of substance abuse
New treatments for disorders of reward circuitry are finally entering psychopharmacology and the prospects for future therapeutics that target malfunctioning in this circuitry have never been greater. So far, psychopharmacologists have been reluctant to embrace new therapeutics for substance abuse, and thus the uptake of new treatments into clinical practice is often slow and many new treatments are still used minimally by many clinicians. Perhaps the lack of effective psychopharmacological treatments until relatively recently has allowed the field to develop therapeutic nihilism to psychopharmacological approaches. Even today, available psychopharmacological treatments for substance abuse remain few and limited in efficacy, as we shall see in this chapter.
However, the time might be right for some paradigm-shifting questions to be posed for the field of substance abuse treatment in the modern era (Table 19-1). For example, should professional psychopharmacologists be first-line treaters of substance abuse, or should this be left predominantly to lay counselors and professionals who have triumphed over their own past substance abuse? Since some treatments may blunt rather than stop all drug abuse behavior, particularly at the initiation of treatment, this leads one to ask: Is total abstinence the only desirable goal of treatment? Finally, is it rational to use drugs to treat drug abuse, or should drugs be seen mostly as crutches to be avoided?
Answers to these questions may determine whether more psychopharmacological practitioners become proactive in identifying and treating nicotine addiction; whether more practitioners start to use treatments for heavy drinking and alcoholism, including those that assure compliance for a month but are rarely used; whether more practitioners start to use opiate partial agonists for “middle class” patients dependent upon opiates who have never taken methadone. Perhaps the psychopharmacology of substance abuse and related disorders of reward is poised at the beginning of a new era, analogous to where psychopharmacology stood for the treatment of depression and psychosis in the 1950s, with major new therapeutics just around the corner.
At this point, understanding of the neuroscientific basis of reward circuitry and the pharmacological mechanism of action of substances of abuse and their drug treatments is exploding. What is known about this exciting field is summarized and reviewed briefly in this chapter. Mastering this will empower the modern psychopharmacologist to make decisions about whether to enter this field of new therapeutics.
TABLE 19-2 Nine key terms and their definitions