The practice by some supplement companies of adulterating herbal and other products with prescription meds has been discussed previously in this forum.
It has gotten so common that the FDA now has 69 different weight-loss supplements (with names like "7 Day Herbal Slim" and "Phyto Shape") flagged for containing such drugs, which include the prescription weight-loss medication sibutramine, as well as various other drugs including the active ingredient in Dilantin and a potentially cancer-causing dye. The idea behind this adulteration apparently is to "juice up" supplements with effective drugs, but even if effective the consumer has no way of knowing what they're getting, and cannot avoid problems if they have health conditions that are a contraindication to receiving such drugs (or are exposed to side effects due to interactions with other drugs they may be taking).
In one case, a company called Confidence Inc. (how appropriate) was caught marketing apple cider vinegar tablets for weight loss which were adulterated with sibutramine. Then they were nabbed again, this time for spiking a product called "Long Weekend" with the equivalent of Viagra. They're apparently still in business.
More on this disgraceful practice here.