It is not unusual for supplements marketed in health-food stores or over the Internet to contain prohibited substances that are not disclosed on the product label. Over the past few years, a significant number of positive tests have been attributed to mislabeled or contaminated supplements.You should be extremely wary of products that, among other things, claim to build muscle, aid in recovery, provide energy or help with weight loss. Because you will be held strictly liable for the consequences of a positive test caused by a mislabeled supplement, the best advice is: you should not take a supplement if there is any doubt as to what it might contain.
If you are unsure what is in a product, do not take it. Ignorance is never an excuse.
The issue of contaminated products has been acknowledged in the new 2015 WADA Code. If an athlete can establish no significant fault or negligence then the sanction can range from a reprimand to a maximum of 2 years.
Managing the Risks of Supplements