However, these products are not regulated by the FDA, so they do not need to prove they work or that they're safe before they hit the market.
Now Consumer Reports is warning some can be dangerous.
Jareem Gunter took a dietary supplement to improve his athletic performance. But he says it landed him in the hospital with liver failure.
"My eyes were jaundiced. My body too, so my hands started turning yellow," Gunter said.
Gunter filed a lawsuit claiming the supplement contained an "illegal synthetic steroid." That suit has now been settled, but Consumer Reports' Nancy Metcalf says dangerous ingredients have been turning up frequently in three different types of supplements.
"The Food and Drug Administration has found synthetic steroids in supplements for body building and prescription drugs in supplements marketed for weight loss and sexual enhancement," Metcalf said.
Some ingredients known to be in products can be hazardous. Consumer Reports worked with an independent research group to identify 12 ingredients consumers should steer clear of.
The top three include aconite, which is used to help joint pain - bitter orange, found in some weight loss supplements - and yohimbe, used for body building and as an aphrodesiac.
RELATED LINK: The 12 supplements you should steer clear of
"These supplement ingredients have been linked by clinical research or case reports to serious side effects, including heart, liver, or kidney problems," said Metcalf.
Not all supplements are bad, and some have been shown to be very beneficial. However it is important to talk to your doctor about which supplements you are taking, and ask if there could be any interaction with medication.