Cocaine is said to be the most reinforcing drug known, as defined by repetitive use. Methamphetamine may be equally or more reinforcing as defined by capture ratio. The effects of cocaine fade sooner than methamphetamine, so cocaine induces more repetitive behavior. Rats will press a bar more times for a dose of cocaine than for any other drug. Rhesus monkeys forced to choose between food and cocaine will choose cocaine almost exclusively, losing weight and continuing their "binge" until either they die or the experiment is discontinued (Aigner & Balster, 1978).

Why does cocaine have this effect? Like methamphetamine, cocaine acts directly on the dopaminergic (dopamine-using) areas of the midbrain that are normally activated by biologically significant events such as victories in combat, pride over creative accomplishments, love and sex. Because such events are followed by great pleasure, an individual will try to repeat them. Cocaine short-circuits the process and brings pleasure without accomplishment. Instead of trying to repeat a biologically adaptive response, individuals try to repeat the intake of cocaine.

What is distinctive about cocaine? Who finds cocaine use most pleasurable?

Cocaine is most pleasurable to people who are depressed or in pain. In this respect, it is like direct stimulation of the so-called pleasure centers of the limbic system. Pleasure and pain normally act as an accelerator and a brake in the so-called hedonic control system of the body (in other words, the pleasure/pain control system). Like all control systems, the hedonic control system seeks an equilibrium or an ideal state (homeostasis) by counteracting disturbances.(See the discussion of biological motives at the beginning of Chapter 9: Motivation.)

How does the concept of a control system explain aftereffects of cocaine?

Heavy use of cocaine, like heavy use of heroin or methamphetamine, leads the body to form a new equilibrium. With cocaine hitting the accelerator all the time, the body starts to compensate by riding the brakes, so to speak. Anti-cocaine substances are secreted into the bloodstream and the areas around neurons to counteract or take up the extra transmitters released by cocaine. If a long-time user stops taking the drug, the result is a rebound effect or "crash" in the body's hedonic control system. This explains why long-term cocaine users say the drug is needed just to feel normal or un-depressed, and life seems unexciting and colorless without it.

Smoking and injecting are the most dangerous forms of cocaine administration, because they carry massive amounts of the drug directly to the bloodstream, producing a quick rush or euphoric sensation that soon wears off. The crash which ensues leaves a person feeling tired and depressed, or just bored. Cocaine users universally report, "You want more." Methamphetamine users report the same sorts of reactions. Ironically, the ability of the drug to produce joy (the so-called honeymoon phase) diminishes just as tolerance begins, because tolerance—the ability to withstand more of the drug, with less reaction— indicates that the body has adjusted to the drug's presence and is compensating or fighting it. At this point pleasure decreases and a user may claim to need the drug just to feel normal.

What is a possible delayed effect of a cocaine meth binge?

Cocaine or methamphetamine use may produce delayed health problems. By the 2000s, health professionals noticed an increase in the number of aneurysms (strokes caused by bulging blood vessels in the brain) among middle-aged people who had binged on cocaine in the 1970s and 1980s. Apparently the high blood pressure spikes of a cocaine binge weakened artery walls in the brain, resulting in an increased tendency to have strokes in later life. Methamphetamine has been observed to produce similar damage, such as tears in artery walls, even in younger people (McIntosh, Hungs, Kostanian, and Yu, 2006).

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