Lead author Dr. Jon Duke, a Regenstrief Institute investigator and assistant professor at Indiana University School of Medicine, and colleagues says the study involved more than 5,600 drug labels and more than half a million labeled effects.
The study, published in the Archives of Internal Medicine, found that the average label contains 70 different side effects, with more commonly prescribed drugs averaging around 100 side effects. A single label contained as many as 525 possible reactions.
Overall, the greatest number of side effects was found in antidepressants, anti-viral medication and newer treatments for Restless Legs Syndrome and Parkinson's disease, the study says.
Generally medications prescribed by psychiatrists and neurologists had the most complex labels, while drugs used by dermatologists and ophthalmologists had the least, Duke says.
"Having a high number of side effects on a drug's label should not suggest that the drug is unsafe. In fact, much of this labeling has less to do with true toxicity than with protecting manufacturers from potential lawsuits," Duke says in a statement. "But having all these labeled side effects can overwhelm doctors who must weigh the risks and benefits when prescribing a medication."