As usual.. Wikipedia has the answer:
There are several naturally occurring plants and vitamins as well as synthetic chemicals that supplement companies claim may produce an increase in testosterone levels. However, the validity of many of these products is questionable due to a lack of valid scientific research showing their effectiveness, and even scientific evidence showing a lack of effectiveness.
Excess testosterone can cause undesirable side effects, such as hair loss and acne, and may be converted into estrogens.
I didn't see the actual supplement you're referring to, without it's name I can't beat google with it untill it coughs up some actual scientific research. I'd suggest googling the name with the word "risks" or "side effects" or something to that effect and see what sites that DO NOT SELL the stuff say.
If all you read are sites that sell the stuff, then all you see is a sales pitch which is almost certain to skew the truth for better sales.
