These 3 types of supplements are 'the most lawless' of the industry, according to a Harvard researcher

Their very name - supplements - makes them sound like a healthy addition to any diet. But most vitamins and dietary powders are unnecessary. Some can even be dangerous, according to Harvard Medical School professor S. Bryn Austin.

Several supplements have been linked with an increase in certain cancers, for example, while others have been tied to an elevated risk of kidney stones.

On June 29, the Food and Drug Administration ordered supplement maker Hardcore Formulations to recall two of its bodybuilding supplements after they were found to be laced with derivatives of anabolic steroids - drugs that can have serious health consequences including liver injury and increased risk of heart attack, stroke, and infertility.

The most dangerous supplements are the ones that claim to increase performance in three broad categories, S. Bryn Austin said at an event organized by the Harvard T. H. Chan School of Public Health. Those categories are: muscle building, weight loss, and sexual performance.

These are "the most lawless of all the categories and where the most problems turn up," Austin said.

The listed ingredients in these supplements can include everything from caffeine to herbal extracts derived from plants like wild mint and olive. But the issue is that some ingredients may not be on the label at all, Austin said.

"What we're concerned about is adulteration - where people are deliberately including ingredients that shouldn't be in there," she said.

The Food and Drug Administration keeps a list of all of the tainted products that have crossed its radar. A large chunk of them are weight loss supplements. The illegal ingredients found in these pills and powders include things like the banned controlled substance sibutramine, which the FDA banned from the market nearly a decade ago. Such supplements have also been found to contain the chemical phenolphthalein, which some research has suggested may be linked to cancer.

Other supplements even include prescription drugs with serious side effects. These can interact in potentially deadly ways with other medications.

"We know that these can be very toxic and have drug interactions," Austin said, adding that "weight loss supplements are making up a majority of events where people end up in emergency rooms."