A study of more than 1.7 million patients found that women had significantly more allergies to common medications than men.

The study, reported in the journal Allergy, analyzed allergies to individual drugs and classes of drugs in patients treated at two hospitals in Boston over more than two decades. None of the reported allergies was more prevalent among men, it found. The research also showed that white patients had significantly more drug allergies than other racial groups.

Researchers used electronic health records to track drug allergies in the patients, treated at Brigham and Women’s Hospital and Massachusetts General Hospital from 1990 to 2013. More than a third had at least one drug allergy, and 31 percent of those patients were allergic to two or more drugs.

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The most commonly reported allergies were to penicillins, sulfonamide antibiotics (sulfa drugs) and opiates. Among women, 15 percent were allergic to penicillins compared with 10 percent of men. Women also had significantly more allergies to other classes of antibiotics, and to NSAIDs, including aspirin and ibuprofen. Among the most common drug-allergy symptoms are hives, rash or fever.

It isn’t clear why women develop more drug allergies than men, including a condition called multiple-drug-intolerance syndrome, lead researcher Dr. Li Zhou, assistant professor in the Division of General Internal Medicine and Primary Care at Brigham and Women’s Hospital, said in an email. Follow-up studies that consider patients’ prescription history and drug exposure may help to explain the gender difference, she said. Racial differences in drug allergies may be biological, she added.

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