Codeine patients take note: How to tell if your body is responding as it should

Are you or is someone you know taking codeine to relieve pain? Then some new information in Public Citizen’s Worst Pills, Best Pills June newsletter will be of interest.

It turns out a substantial minority of people using codeine may be at risk of getting inadequate pain relief or experiencing serious side effects because of certain genetic factors and other medications they may be taking.

The reason codeine works as a painkiller is because the body converts it into morphine in the liver using an enzyme called CYP2D6. However, not everyone has the same level of CYP2D6 activity. Some have activity that is higher or lower than normal, which could result in an excessive or inadequate response to codeine.

If you have lower CYP2D6 activity and are taking codeine, you’re not at any heightened risk. You’ll probably just notice that taking codeine doesn’t work very well at relieving your pain. The potentially more dangerous situation involves people with higher than normal CYP2D6 activity, because their bodies produce greater amounts of morphine from codeine. Serious side effects caused by excessive morphine in the blood stream can include severe constipation, respiratory depression and excessive sedation.

The big drawback to this discovery is, of course, the fact CYP2D6 enzyme testing is currently not affordable or routinely available. However, Dr. Sidney Wolfe, director of our Health Research Group, says there are still things patients can do to determine whether their bodies are responding normally to codeine. He says patients who do not experience an expected painkilling effect should report this issue to a prescribing physician. He also says first-time codeine users should look out for the signs of an excessive response.

You should also tell your doctor all other drugs you’re taking. Some, including the nonprescription medication Benadryl (diphenhydramine), can inhibit CYP2D6 activity.

And if you still have questions, Public Citizen is here to help. Check out the full article on codeine on our Worst Pills, Best Pills Web site.