Mary Ann Johnson will never forget the day the nurses were ready to wheel her 16-year-old autistic son into the operating room.
He was about to have open-heart surgery, but at the last minute, the surgical team had to call off the procedure when they learned Johnson had given her son the supplemenet St. John's Wort for depression.
What she didn't know was that the St. John's Wort was also thinning her son Adam's blood and could have spelled disaster during surgery.
"Poor Adam was a wreck about it," Johnson said. "And so was our whole family."
She's not alone in the confusion about supplements -- in a recent study, 66 percent of participating parents said they thought supplements did not interact with other medications.
"When you pick up a bottle of an herbal med, does it contain what it says it contains? Are the ingredients the actual ingredients?" asked Dr. Lawrence Rosen, a founding member of the American Academy of Pediatrics.
Many companies selling the products have bypasssed parents altogether and are marketing them to teens directly.
"The model of tobacco companies is what many companies are following," said Dr. Jordan Metzl of the Hospital for Special Surgery in New York. "I think it is really frightening."
When 17-year-old football player Aaron Ryel was tired of getting tackled, he went on the Internet and immediately found ads for body-building supplements.
His parents were aware that the high school senior spent around $1,000 on the supplements and used them to increase his weight from 164 pounds to 210.
"We just asked him if it was safe and made sure there were no side effects," said his father, Rick Ryel. "We didn't tell him he could do it; we didn't tell him he couldn't."
But doctors point out kidney failure and other complications have already been linked to body-bulking supplements.
"Many companies are looking primarily at their bottom line, and they really don't care much about health issues," Metzl said.