A range of designer analogs of licensed PDE5 inhibitors such as sildenafil and vardenafil have been detected in recent years in over-the-counter herbal aphrodisiac products,[4][5][6][7] in an apparent attempt to circumvent both the legal restrictions on sale of erectile dysfunction drugs, which are prescription-only medicines in most Western countries, and the patent protection which allows sale of these drugs by competitors only with permission from the patent holders (typically, under a license from the inventors) and to introduce efficacy into otherwise ineffective herbal products. These compounds have been demonstrated to display PDE5 inhibitory activity in vitro and presumably have similar effects when consumed, but have undergone no formal testing in either humans or animals, and as such may represent significant health risks to consumers of these products due to their unknown safety profile.[3][8] Attempts to ban such ingredients have not been successful for the most part, many jurisdictions having laws restricting chemical analogs but only those of narcotics and doping agents. However, at least one court case has resulted in a product being taken off the market.[9]
^Blok-Tip L, Zomer B, Bakker F, Hartog KD, Hamzink M, Ten Hove J, et al. (August 2004). "Structure elucidation of sildenafil analogues in herbal products". Food Additives and Contaminants. 21 (8): 737–48. doi:10.1080/02652030412331272467. hdl:10029/11381. PMID15370823. S2CID45568769.
^ abPoon WT, Lam YH, Lai CK, Chan AY, Mak TW (October 2007). "Analogues of erectile dysfunction drugs: an under-recognised threat". Hong Kong Medical Journal = Xianggang Yi Xue Za Zhi. 13 (5): 359–63. PMID17914141.
^Venhuis BJ, de Kaste D (October 2012). "Towards a decade of detecting new analogues of sildenafil, tadalafil and vardenafil in food supplements: a history, analytical aspects and health risks". Journal of Pharmaceutical and Biomedical Analysis. 69: 196–208. doi:10.1016/j.jpba.2012.02.014. PMID22464558.
^Zou P, Oh SS, Hou P, Low MY, Koh HL (February 2006). "Simultaneous determination of synthetic phosphodiesterase-5 inhibitors found in a dietary supplement and pre-mixed bulk powders for dietary supplements using high-performance liquid chromatography with diode array detection and liquid chromatography-electrospray ionization tandem mass spectrometry". Journal of Chromatography A. 1104 (1–2): 113–22. doi:10.1016/j.chroma.2005.11.103. PMID16364350.
^Hou P, Zou P, Low MY, Chan E, Koh HL (September 2006). "Structural identification of a new acetildenafil analogue from pre-mixed bulk powder intended as a dietary supplement". Food Additives and Contaminants. 23 (9): 870–5. doi:10.1080/02652030600803856. PMID16901855. S2CID35240702.