Hundreds of dietary supplements contain dubious variants of sildenafil (the generic name for VIAGRA): the regulatory authorities of some countries are increasingly issuing warnings about adulterated dietary supplements - about products that are advertised as being natural and purely herbal, but in which laboratory tests have detected chemical active substances. Meanwhile, the "Adulterated" database of the Gute Pillen - Schlechte Pillen* [Good Pills - Bad Pills] consumer magazine (www.gp-sp.de -> Gepanschtes) lists approximately 1000 dietary supplements that have come to its attention, yet this is probably only the tip of the iceberg. Inhibitors of phosphodiesterase (PDE) type 5, such as sildenafil (VIAGRA) have been discovered in more than 40% of these products, and in some cases they are present at higher doses than are used medically. Men, who need to avoid active substances such as sildenafil, for example because they use nitrate preparations for angina pectoris, are particularly likely to resort to products that are being marketed as "natural" treatments for erectile dysfunction. It is these men who are especially at risk, because combining PDE inhibitors with nitrate preparations can cause blood pressure to decrease to a dangerous level. Companies, which adulterate products in this way are increasingly using chemical variants of phosphodiesterase inhibitors, which are not used as medicines and for which there are no routine tests. Their motive is to make analysis of admixtures more complicated and their legal assessment more difficult. About 50 different variants have so far been detected in dietary supplements. (Unexpected) side effects are likely, for example if the chemicals are less selective for PDE 5 than conventional PDE-5 inhibitors. For instance acetildenafil has been seen causing vision impairment. It produces far stronger inhibition of the PDE 6 present in the retina than sildenafil. Toxicological concerns also exist for other reasons, including the potential for alkylating compounds to arise through metabolism, such as happens with chlorodenafil (VENHUIS, B.J., de KASTE, D.: J. Pharm. Biomed. Anal. 2012; 69:196-208). In view of the incalculable risks, it is recommended to inform potential users of the following rule of thumb: There are only two types of dietary supplements for impotence, namely those that are probably safe but ineffective, and those that are potentially effective but risky (COHEN, P.A., VENHUIS, B.J.: JAMA Intern. Med. 2013; 173: 1169-70).

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