Coatings of many drugs and supplements contain harmful chemicals called phthalates, says study.
These chemicals have been linked to a variety of hormonal and reproductive problems in both rats and people.
Scientists can't yet say how levels of phthalates in pills might translate into health risks. But the scientists behind the work said, pregnant women and children might want to be cautious especially those who take regular doses of medicine for chronic conditions.
It may be impossible to completely avoid phthalates in medicines, though, because not all phthalate-containing drugs mention inactive ingredients on their packaging. And researchers don't want people to stop taking the pills they need.
Instead, the new work points to the need for both further research and possible action by regulating agencies.
"Since medications are an important component of health care, I would not ask the consumer to make these decisions," discovery News quoted Russ Hauser, a reproductive physiologist at the Harvard School of Public Health and one of the authors of the new study as saying.
"This decision about whether phthalates should be used in medications should be made at the federal level by the F.D.A," he added.
Phthalates describe a class of chemicals that have a wide range of industrial uses. As ingredients in plastics, they provide flexibility and resilience. In coatings on capsules and pills, they can help regulate the release of drugs over time or the delivery of active ingredients to specific areas in the digestive tract where it is most useful for them to be absorbed.
In total, the search included between 500 and 1,000 supplements and drugs, both prescription and over-the-counter.
Of those, the team found more than 100 contained two forms of phthalates that have been shown to have deleterious health effects in studies on animals and human infants.
Called dibutyl phthalate (DBP) and diethyl phthalate (DEP), these chemicals affect the reproductive tracts of developing males, leading to hormonal, fertility and reproductive problems, said Shanna Swan, a reproductive epidemiologist at the Mount Sinai School of Medicine in New York.
Among other studies, she has found that preschool boys who had been exposed to the highest levels of DBP in the womb were least likely to choose typically male toys.
It's too early to know what the health risks are, but pregnant women are the biggest source of concern, Swan said, especially if they take coated medicines for long-term issues.
The study was reported in Environmental Health Perspectives.