Most of us know that generic and underground drugs often contain active ingredients that are not listed on the label. Just like tainted herbal or nutritional supplements.
One of the best examples in this case are drugs/supplements to fight erectile dysfunction. Over 45 different versions of drugs in the same class of Viagra have now been found in male sexual supplements. A Dutch study found that 75% of the products sold in the Netherlands contained at least one analogue, or chemical variant that has the same effect as Viagra.