Does Dopamine Play a Role in Addiction?
Dopamine doesn't force someone to stick a needle into his or her arm, smoke meth or take a hit from a crack pipe, nor does it create the pleasure that a drug user experiences from getting high. But dopamine does play a role in drug abuse and addiction, by reinforcing the effects of using those drugs.
When a person gets high, it causes a surge in production of dopamine in the neurons in the striatum, including the nucleus accumbens, structures that are part of the brain's reward network. That increase in the chemical enables neurons to make more connections, and plays an important role in programming the brain to connect drugs with pleasure, so that it develops an expectation of a reward and motivation to take them again [source: Volkow, Fowler and Wang, et al.].
"Large surges of dopamine teach the brain to seek drugs at the expense of other, healthier goals and activities," warns an article on the National Institute on Drug Abuse's website.
But while dopamine increases when someone uses certain drugs, not everybody who experiences that surge necessarily becomes an addict. Instead, scientists believe, dopamine acts in combination with a range of other genetic, developmental and/or environmental influences to program some people's brains to develop a compulsion to take those drugs. Imaging studies, for example, have found that people who turn into addicts may already have differences in their dopamine circuitry that make them more vulnerable to getting hooked [source: Volkow, Fowler and Wang, et al.].
The dopamine produced from using drugs is much more intense and long-lasting than the dopamine response from something like eating or another normal activity. Also unlike eating, the dopamine response from drugs doesn't stop when the act is over. The overflow of dopamine is what produces the high.
When an addict uses drugs repeatedly, his or her brain changes in response. It tries to compensate for the surge in dopamine production by shutting down some of its dopamine receptors. But that only exacerbates the situation. The brain is still programmed to want the pleasure that the drugs created, so an addict has to use more and more of the drug to replicate the effect. Additionally, shutting down dopamine receptors reduces the amount of pleasure that an addict gets from any activity, not just taking drugs — a condition called anhedonia. That also may drive a person to shoot up more heroin or smoke more and more meth, because nothing else feels good anymore.
Finally, having fewer dopamine receptors is associated with an increase in impulsivity, which may lead an addict to engage in increasingly reckless behavior in pursuit of a high [source: Butler Center].