Drugs and Addictive Behavior

¶ … Hijacked Brain

You can be both physically dependent (addicted) and psychological dependent on a substance. Or you have only one type of dependence. For instance, you might be psychologically dependent on your teddy bear or a cup of chamomile tea at bedtime, and believe you can't possibly go to sleep without it. How do you know if you are physically dependent upon a substance?

Probably the most obvious symptom of physical addiction is the onset of symptoms of withdrawal, if the addict attempts to stop using the drug. Psychological dependence may produce physical symptoms caused by the anxiety that is created by stopping the comforting behavior. But the symptoms of physical addiction are so unpleasant that even if the individual wishes to stop using drugs, because his or her liberty, job, or family is at risk, it is still extremely difficult to do so, because the effects on the body of withdrawal are so unpleasant.

Which neural pathway (brain circuit) do potentially addictive substances act upon? Which brain chemical (neurotransmitter) is involved?

Addictive substances affect the neural pathways that release dopamine and stimulate the release of dopamine in the brain in the limbic system of the brain. Or they may prevent dopamine from being reabsorbed by blocking the brain's dopamine receptors. Dopamine is the pleasure or thrill-seeking chemical released during times of intense stress or pleasure. An increase in dopamine provides a sense of reward that occurs when the addictive substance is introduced and reintroduced into the abuser's body. Eventually, the brain adapts to the addictive substance, and there is a corresponding decrease in the brain's ability to produce dopamine naturally or an increase in dopamine receptors, reducing the natural level of dopamine in the brain. This reinforces the addictive behavior, as now the addict must take the drug to feel normal, not simply to feel 'good.' Very often the addict will increase the dosage, to experience the old 'high.'