Possible Harmful Effects From Prolonged Methadone Use

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New research from the Norwegian Institute of Public Health shows that methadone affects the brain and impairs the attention of experimental animals. Methadone has been used to treat heroin addicts for nearly 50 years. Yet we have surprisingly incomplete knowledge about possible harmful effects from prolonged use.

Possible Effects

In general, opioids such as heroin and morphine are known to weaken intellectual functions such as learning, memory and attention. “For ethical reasons, methadone cannot be tested in long-term studies of healthy volunteers. It is also difficult to draw reliable conclusions from studies with methadone patients, because these studies often encounter methodological problems. Therefore, animals were used in the research.”

New Study

“In a new study, Andersen and colleagues treated rats daily with methadone for three weeks and studied the rats' attention. The researchers measured how long the rats examined a new object introduced into their cage. The results show that the treatment clearly reduced the attention of the animals. This was true both when the rats had methadone in the body and, more importantly - a day after the last treatment, when the methadone had been excreted.”


"The fact that the attention is impaired even after the drug was no longer present in the body suggests that methadone causes changes in brain cells. We do not yet know exactly what the changes are and how long-lasting they will be" says Andersen.