

Gastric bypass can affect how medications work

Q: I suffer from chronic back pain that requires ongoing pain medication, but the medication only works for two to three hours at a time. Years ago, I had gastric bypass surgery. How does this surgery affect how medications work? Is it true that it can limit full absorption of time-release medication?

A: Many medications can be absorbed normally after gastric bypass surgery. But certain drugs, including some types of time-release medications, require careful monitoring in people who have had gastric bypass.

Gastric bypass is a type of bariatric, or "weight-loss" surgery that works by decreasing the amount of food you can eat at one time and by reducing the body's ability to absorb nutrients from food.

In the most common type of gastric bypass, called a Roux-en-Y gastric bypass, the top portion of the stomach is sealed off from the rest of the stomach, creating a pouch about the size of a walnut. The new pouch can hold only about 1 ounce of food, rather than the 3 pints of food the stomach can normally hold. The small intestine is then transected and sewn directly onto the small remaining stomach pouch. The rest of the stomach and the first 3 feet of the small intestine, where most nutrient absorption occurs, are bypassed so food goes from the small stomach directly into the middle section of the small intestine.

Despite these changes to the stomach and intestine, many medications are absorbed normally in people who have had gastric bypass surgery, including most pain medications. In some specific situations, though, medication absorption can be a concern. For time-release medications, also called controlled-release medications, the problem involves the way the medicine is broken down in the stomach and released into the body.

With controlled-release medications, rather than taking multiple pills during the day, you take only one or two pills per day that slowly release medicine over time. The controlled-release pills use several different methods for leaking the drug they contain. After gastric bypass, reduced acidity or a change in the concentration of enzymes in the intestine can drastically alter how this medication is released, which can prevent the drug from reaching the bloodstream.

Certain types of antidepressant drugs may also be affected by gastric bypass surgery. Following gastric bypass, some people may need to have their dose of antidepressant medication modified, or they may need to switch to a different type of antidepressant.

In addition, medications designed to regulate a person's heartbeat and prevent an irregular heartbeat, called anti-arrhythmic drugs, need to be closely monitored in people who have had gastric bypass, as their absorption may change due to the surgery. The same is true for people who've had an organ transplant and are taking immunosuppressive drugs to prevent their bodies from rejecting the new organ. Their medication dosages should be followed closely.

Even with drugs that require monitoring after gastric bypass, absorption should not be a major problem to overcome. In many cases, a change in dose or medication type is all that's needed.


If you feel your medications are not working the way they should, make an appointment to see your doctor. Bring a list of all your current medications and dosages to that appointment, so you can review them together.

This article was written by Dr. Michael Sarr, with Gastroenterologic and General Surgery at the Mayo Clinic in Rochester, Minn. Distributed by Tribune Media Services.

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