By binding to enkephalin receptors, opiates like morphine enhance the pain-killing effects of enkephalin neurons. Opiate tolerance can be explained, at least in part, as a homeostatic response that reduces the sensitivity of the system to compensate for continued exposure to high levels of morphine or heroin. When the drug is stopped, the system is no longer as sensitive to the soothing effects of the enkephalin neurons and the pain of withdrawal is produced. This accounts for the suppressive effect opiates have on breathing. In fact, if the receptors are already occupied by, for example, heroin molecules, naloxone will push the heroin molecules off and quickly rescue the patient from a drug overdose.
Naltrexone is used to help recovering heroin addicts stay drug-free.
Tranquilizers Tranquilizers act like sedatives in reducing anxiety and tensions but do not have their sleep-inducing effect. The group is often subdivided into the major tranquilizers and minor tranquilizers. These are used to treat schizophrenia , a common and devastating mental disease. They act by binding to one class of receptors for the neurotransmitter dopamine . The drugs block the action of dopamine, and in a homeostatic response, the neurons increase their activity.