Opioids are drugs derived from the plant Papaver somniferum, the opium poppy. Opiates, sometimes called narcotics, are well-known for their powerful analgesic effects. According to the website PubMed, methadone is a long-lasting pain reliever effective for the treatment of moderate to severe pain that has been unresponsive to other treatments. Methadone is also administered to some people undergoing drug rehabilitation for the use of other opiate drugs because it helps to provide relief from uncomfortable withdrawal symptoms.
Reward and Reinforcement
The textbook "Molecular Neuropharmacology" explains that certain pathways within the brain are responsible for processing information related to reward and reinforcement. Reward can be defined as something positive or desirable while reinforcement refers to the environmental conditions at the time of reward. Reinforcement serves to direct behavior such that we repeat experiences that are rewarding and avoid experiences that are unpleasant. Methadone is rewarding because it provides relief from unpleasant stimuli, such as pain or withdrawal symptoms. The behavior--taking methadone--is reinforced by the positive effects of the drug.
Opioid Receptors in the Nervous System
Brain cells, called neurons, are able to respond to methadone because they possess special proteins known as opioid receptors. Scientists have identified three types of opioid receptors, called mu, delta and kappa. The text "Neurobiology of Addiction" explains that the reinforcing effects of methadone and other opioids stem from interaction with the mu receptor. Cells that possess the mu receptor are found in areas of the nervous system that communicate messages of pain and also messages of reward.
Dependence
The body is able to adapt to a person's long-term methadone use by changing the way cellular mu receptors respond to the drug, according to "Neurobiology of Addiction." This results in the development of drug tolerance, whereby higher dosages of methadone are needed in order to experience the desired effects. This evolves into drug dependence, evident when withdrawal symptoms appear following discontinuation of the drug.
Withdrawal
Withdrawal symptoms are a physiological reaction to an upset in the metabolic balance of cellular activity, according to the text "Clinical Manual of Addiction Psychopharmacology." When a person develops a tolerance to methadone, it is because of changes that are made by the cells. Cells make their opioid receptors less sensitive or decrease the number of opioid receptors that they possess. These changes allow cells to function almost as if methadone is not present at all. But when a methadone-dependent individual suddenly stops taking the drug, the cells are unable to communicate normally, causing a variety of physical symptoms. Withdrawal symptoms from methadone include excessive yawning, tearing of the eyes, runny nose, sweating, muscle tremors, stomach upset, bone pain and depression.
Methadone for Addiction
Despite methadone being an addictive drug, it has shown promise as a treatment for people addicted to other opioid drugs. The Centers for Disease Control and Prevention cites methadone maintenance therapy as the most effective treatment for opioid drug addiction. Most patients who are accepted into methadone maintenance rehabilitation programs are injectable drug users who have a history of heroin abuse. Methadone is effective because it eliminates the unpleasant symptoms of drug withdrawal without impairing cognitive and motor function. Additionally, elimination of injectable drug use helps to prevent the spread of HIV and other communicable diseases.
References
- PubMed Health: Methadone
- "Molecular Neuropharmacology: A Foundation for Clinical Neuroscience (2nd Edition)"; Eric Nestler, Seven Hyman and Robert Malenka; 2009
- "Neurobiology of Addiction"; George F. Koob and Michel Le Moal; 2006
- "Clinical Manual of Addiction Psychopharmacology"; Henry R. Kranzler, M.D. and Domenic A. Ciraulo, M.D.; 2005
- The Centers for Disease Control and Prevention: Methadone Maintenance Treatment
