The Disease Model of Drug Addiction
It is not disputed that some substances cause withdrawal symptoms after repeated use, leaving the user in distress if they stop using. Where scientists differ is over the extent to which certain substances can be said to rob the user of self control, causing not only withdrawal— but a drug addiction, defined as "a behavioral pattern of drug use, characterized by overwhelming involvement with the use of a drug (compulsive use), the securing of its supply, and a high tendency to relapse after withdrawal."
In the 19th century, drug addiction was regarded as a sign of akrasia, immorality, or weakness of the will. However 20th century brain research replaced this moral model with a disease model of addiction, according to which addiction to a drug is a by-product of the chemical structure of the drug itself. According to social psychologist Stanton Peele, the disease model states that "olerance, withdrawal, and craving are thought to be properties of particular drugs, and sufficient use of these substances is believed to give the organism no choice but to behave in these stereotypical ways." This view of drug addiction is reflected in the policies of the War on Drugs and in slogans such as "Heroin is so good. Don't even try it once," or "Crack cocaine is instantly addictive."
Scientists adhering to the disease model believe that behavior is "the business of the brain," according to Avram Goldstein, Professor Emeritus of Pharmacology at Stanford University, and a leading researcher into drug addiction. Goldstein writes that the site of action of heroin and all other addictive drugs is a bundle of neurons deep in the brain called the mesolimbic dopaminergic pathway, a reward pathway that mediates feelings of wanting and motivation. Within this pathway, heroin causes dopamine neurons to release dopamine, a neurotransmitter that determines incentive salience and causes the user to want more. Dopamine neurons are normally held in check by inhibitory neurons, but heroin shuts these down, allowing the dopamine neurons to become overstimulated. The brain responds with feelings of euphoria, but the stimulation is excessive, and in order to protect itself against this, the brain adapts by becoming less sensitive to the heroin.
This has two consequences, according to the disease model. First, more heroin is required to produce the high, and at the same time, the reward pathway becomes less sensitive to the effects of endorphins, which regulate the release of dopamine, so that without heroin, there is a persistent feeling of sickness. After repeated intake, the user becomes tolerant and dependent, and undergoes withdrawal symptoms if the heroin supply is terminated. As the feelings of withdrawal worsen, the user loses control, writes Goldstein, and becomes an addict.
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