Methadone: Physiological effects

Last modified: Monday, 1. June 2009 - 6:06 am

Methadone, like all opiates, is a chemically simple compound that has a variety of effects on those who take it. But while other opiates exert powerful euphoric effects on a person by acting very much like chemicals called endorphins and enkephalins, methadone produces only a mild (or no) euphoria, to which patients quickly become tolerate. Endorphins and enkephalins are naturally produced inside the brain. When released in the brain’s reward system, they produce a mind reward and users feel good as a result. Methadone and other opiates mimic these natural brain chemicals, which is why they are so addicting.
Scientific research has shown that methadone and other opiates have specific areas, or sites, that they attach to in order to exert their influence on the brain and body. These sites, called receptors, are classified as mu, delta, and kappa, depending on what body functions they influence. Opiate activation of mu and delta receptors seems to influence mood, respiration, pain, blood pressure, and gastrointestinal functions. Kappa receptors appear to be more involved in the perception and aversion to pain. The degree of methadone’s effect on these receptors can vary widely between individuals, however, there are certain effects that are almost universal.
Nausea is a side effect of all opiates. People who take opiates, including methadone, for a long period of time generally develop a tolerance for its nauseating effects. Vomiting, while common with other opiates such as heroin, is actually a rare side effect of methadone. These side effects are due to the stimulation by opiates of the part of the brain called the medulla, which controls nausea and vomiting.
Another important side effect of all opiates on the central nervous system is respiratory depression. This is caused by an inhibitory effect on the brain stem, which is the part of the brain that controls breathing and other involuntary bodily systems such as heart beat, etc. Like nausea and vomiting, people who take methadone and other opiates normally develop a tolerance to this side effect. However, even people who have taken methadone for a long period of time can develop major respiratory depression.
Cough suppression is another side effect of opiates. In fact, some opiates such as codeine are specifically marketed as cough suppressants. Other less common side effects of methadone include convulsions with very high doses, and a heavy feeling in the arms and legs. While not fully understood, it is thought that this side effect is due to the methadone causing increased blood circulation to the peripheral blood vessels of the body, especially to the arms and legs.
One of the most annoying physiological side effect of methadone use is a feeling of dryness in the mucous membranes of the mouth, eyes, and nose. This is caused by methadone reducing the secretion of saliva, tears, and mucous. Regular users of methadone refer to the dryness of the mouth as “cotton mouth,” since the feeling is akin to having one’s mouth stuffed full of cotton.
Methadone and all other opiates also have the unwanted physiological side effect of producing constipation. Generally, involuntary movements, or waves, of the muscles in the small and large intestines propel fecal matter through the intestines and out of the body. However, methadone and other opiates significantly slow these involuntary movements, and result in constipation. Even after long usage, many users of methadone will continue to report continued constipation.
A very visible physiological effect of methadone and all other opiates is the constriction of a person’s pupils. The pupils, which are the black center of the eye, can be likened to lens on a camera. When pupils are wide open, then more light can pass through. When the pupils are constricted, very little light can pass through. Persons who are on methadone often have pupils that are quite small, making it very difficult for the person to see in anything but bright light.
There are other Physiological effects of methadone for which there is no known mechanism. In women who use methadone, there can be changes seen in their menstrual cycle. It has been hypothesized that these changes are due to methadone’s effect on the hormones that regulate menstruation, but this has not yet been proven.
Another side effect of methadone is a change in a user’s sexual desire and function. One theory is that opiates decrease testosterone levels in both men and women; one small study of 29 methadone users found testosterone levels to be decreased by 40%. Methadone also inhibits sexual function by increasing the tone in the muscles surrounding the urethra and therefore causing a delay in orgasm in men.
It is generally thought that methadone is extremely dangerous for women who are pregnant. The fact is that there are no well-researched studies showing any adverse Physiological effects for pregnant women who are using methadone for heroin withdrawal. However, while the risk for pregnant women may be minimal, there are very real physiological risks for their babies.
The first problem for the baby of a woman who is using methadone is a higher risk of low birth rate. Most studies show that babies born to women who are using methadone for heroin detoxification have a 25% greater risk of low birth weights than babies whose mothers were not using methadone. It is thought by some researchers that methadone itself somehow causes babies to be born underweight, but the majority of drug addiction specialists feel that the higher incidence of low birth weight seen among methadone users is due in fact to social factors such as poor nutrition, smoking, and poverty.
Babies who are born to mothers who are using methadone are at high risk of experiencing a syndrome known as the methadone withdrawal syndrome. This syndrome usually occurs within 48 hours of birth, but can be seen anytime during the first two weeks of birth. Symptoms are quite variable, but generally include irritability and sleep disturbances; prolonged sneezing; loud, shrill cries; watery stools; hyperactivity; poor weight gain; and aversion to bright lights.
Besides the classical withdrawal signs, there are other reported physiological problems in babies born to mothers who are using methadone. Some studies have reported that there is a higher rate of infant mortality and SIDS (sudden infant death syndrome) in babies who are born to methadone-using mothers. However, these studies were done in the 1970s, when there was a generally higher rate of infant mortality. Subsequent studies have failed to prove a definitive relationship between methadone use by pregnant women and a subsequent increase in death rates in their infant offspring.
Many physicians who do not treat opiate addicts on a regular basis believe that methadone inhibits and interferes with the functioning of a person’s immune system. While it is true that some of the shorter acting opiates like heroin do inhibit a person’s immune system, and thus make them more prone to infections, methadone does not inhibit the immune system. This is an important fact, especially in light of the fact that many ex-heroin users have HIV and AIDS. There are even some researchers who believe that methadone, by ways still unknown, may even help restore the functioning of the immune system in patients with HIV.
Harmful side effects
The harmful side effects of methadone, if taken in controlled conditions of a heroin detoxification program, are actually very small. The three main side effects of methadone use are tooth decay, constipation, and accidental overdose. Over half the users of methadone report problems with their teeth related to their methadone usage. Methadone use makes users more prone to tooth decay because methadone in a treatment clinic is generally given as a syrup-based mixture that has a high-sugar content, and is also acidic. Also, methadone itself inhibits the production of saliva in the mouth, which indirectly promotes the production of plaque. To help prevent tooth decay in methadone users, researchers are formulating water-based, sugar-free solutions of methadone, and promoting a low-sugar diet along with regular dental checkups for long-term users of methadone.
Chronic constipation is also another troublesome side effect of prolonged methadone use. As discussed previously, methadone significantly slows the involuntary movements of the small and large intestines. By consuming a high-fiber diet and plenty of water, chronic users of methadone can reduce, but not eliminate, the occurrence of constipation.
The third and most serious side effect of long-term methadone use is the danger of an overdose. Methadone is one of the most powerful opiates, and with its slow onset of action and long half-life, that is, the time it stays active in the body, it can cause overdose, even in chronic users. Early signs of methadone overdose include nausea and vomiting, drowsiness, reduced heart rate, and pinpoint pupils. Signs of a more severe overdose include breathlessness and convulsions, which may result in death. To help prevent a methadone overdose, people should follow the advice of the physician or treatment specialist who provides methadone to them, and they should not mix methadone with other drugs, especially tranquilizers or alcohol. All suspected cases of methadone overdose should immediately be taken to the nearest hospital emergency room.
Long-term health effects
The long-term health effects of methadone, if taken in the controlled conditions of a methadone maintenance program, are minimal. Through the study of thousands of patients, researchers have shown that while some physiological changes do occur in people taking methadone, problematic long-term health effects during prolonged treatment are very rare. In fact, the most important long-term side effect seems to be that there are significant improvements in the general health of heroin addicts who enter a methadone maintenance program.

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