Is Your Energy Bar Messing Up Your Meds?

Six surprising medication snafus, resulting in poor workouts, bad dreams, underdosing—and maybe even an early grave.

By Stacey Colino
Rx medication prescription meds pink bottle pills pharmacy picture
Photograph: Ann Cutting

THE FDA can regulate a pill’s ingredients and dosage, but no government agency can control the other side of the medication equation: you. The effectiveness and safety of many widely used drugs are influenced by your age, weight, health, body fat and, especially, your gender, says Marianne J. Legato, MD, a professor of clinical medicine and head of the Partnership for Gender-Specific Medicine at Columbia University. For instance, women metabolize several drugs, such as the steroid prednisolone, faster than men; for that reason, women may need to take higher doses of them than men do.

Women also experience more side effects than men when taking the same medications. The antianxiety medicine diazepam (better known by its brand name, Valium) impairs psycho-motor skills more in women than in men; anti-histamines are more likely to make women want to take a nap. And fertile women have higher odds of experiencing skin reactions, especially rashes, to various antiseizure medications. Add up all the effects, and it turns out that women have a 50 to 70 percent higher risk of developing an adverse reaction to a drug than men do, according to an estimate from the Society for Women’s Health Research (SWHR).

While it’s hard to pinpoint why the sexes differ in their reactions to specific drugs, some general mechanisms are known. Women have a more active version of CYP3A4 enzymes, which are crucial for the metabolism of drugs by the liver; that’s one reason women process and clear some drugs comparatively quickly, explains Legato. Alternatively, women’s higher percentage of body fat means that drugs stored in fat tissue may have a longer-lasting effect in women than in men.

The bottom line: Women need to be especially vigilant about taking drugs, whether over the counter or prescription. Here are the most important nuances that your doctor or pharmacist may not take the time to spell out—and that you may not notice on the information sheet that comes with the product.

If you do encounter unusual symptoms that you think are drug related, tell your health care provider right away. “Your doctor should know if these are normal side effects or something potentially worrisome,” says Jennifer Wider, MD, medical adviser to SWHR and coeditor of The Savvy Woman Patient. Always consult your physician before you change your medications.


Cardiac arrhythmia, aka irregular heartbeat, resulting from drugs is probably the most studied side effect in women. “Since females tend to have a longer QT interval—the time it takes for the heart to relax between beats—drugs that further lengthen the interval could lead some women to have fatal arrhythmias,” says Legato. Medications with this potential include some commonly used antibiotics (like erythromycin, clarithromycin and sparfloxacin), anti-fungal drugs (fluconazole and others in the azole class), antipsychotics (such as thioridazine and pimozide) and antidepressants (particularly the older tricyclics, now used more often for migraine, irritable bowel syndrome and chronic pain than for mood elevation). Ironically, several anti-arrhythmia medications (such as disopyramide and sotalol) can contribute to irregular heart rates. At particular risk for developing drug-induced arrhythmia are people with heart disease or an electrolyte imbalance due to abnormal levels of minerals in the body, according to a 2008 review by researchers at Brown University.

PROTECT YOURSELF Make sure your physician knows if you have a heart-rhythm abnormality or a family history of heart problems. If she prescribes a new medication for you, ask whether it has been associated with any rhythm disturbances. Also, inquire if there are other drugs you should avoid while using a particular medication, because sometimes a combination of drugs can prolong the QT interval, Legato advises. When taking a new med, be on the lookout for any cardiovascular symptoms, such as heart palpitations and an out-of-breath feeling.


First Published August 22, 2011

Share Your Thoughts!


Prafulla More11.18.2011

Hi, Stacey Colino!A fantastic article from you on a very important health related issue.It is very serious to know that the effectiveness and safety of many widely used drugs are influenced by your age, weight, health, body fat and, especially, your gender.Looking at dangerous side effects of commonly used medicine One can say that The Cure is worst than disease.
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