One exception is black cohosh, described as perhaps the most popular herbal product.
Dietary supplement, any vitamin, mineral, herbal product, or other ingestible preparation that is added to the diet to benefit health.
In a letter to groups representing herbal product makers, the agency said it was aware of dietary supplements derived from three types of comfrey that contain toxic alkaloids.
The penalty handed down by the US Anti-Doping Agencameame two months after Hamilton admitted taking a herbal product to combat depression, knowing it included a steroid.
The report said qat was a herbal product made up of leaves and shoots of the shrub Catha edulis, which releases a mild stimulant after being chewed for about an hour and three-quarters.
A test of 13 brands of a popular herbal product, Sam-e, found that only seven had contents in keeping with the label, according to Consumerlab.com, an online independent group that tests supplements sold in this country.
John Cardellina, vice president for botanical science at the Council for Responsible Nutrition, a trade group for herbal product makers, said the only part of the Consumerlab analysis he agreed with was that "garlic is a very confusing supplement".
Nevertheless, more than three-quarters of women who currently use them said they were confident that they were taking the right dose, and half said they knew how long it would take for the herbal product to start working.
He said that to approve an herbal product as a drug, the federal agency insisted that its manufacturer provide the same proof of safety and efficacy as other new drugs.
The penalty, handed down by the United States Anti-Doping Agency, came two months after Hamilton, 38, admitted taking an herbal product to combat depression, knowing it included a steroid.
Isobel McKenna, lead manager at the Thames Reach hostel where Nick lived, says her clients report mixed experiences with spice, a herbal product sprayed with molecules that have an affinity to cannabis.
