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Sildenafil in supplements – policing the food-pharma border

Thirty years ago, perhaps the only dietary supplement familiar to most consumers was cod liver oil, alongside the occasional effervescent drinks tablet after a big night out. Over the past few years, however, these products have broken out of the health food stores onto the shelves of mainstream supermarkets – today, over three quarters adults in the United States report taking at least one dietary supplement (1), and the industry is expected to be worth over $270 billion (US) by 2027. (2)



Of course, with such a wide range of products on the market, it can be difficult to pin down exactly what constitutes a dietary supplement, a term used to describe products as disparate as algae-containing tablets and whey-based protein powders. The Dietary Supplements Health and Education Act of 1994 (DSHEA) was set up to solve this problem, defining a dietary supplement as a consumable product other than tobacco that contains one or more of the following dietary ingredients:


- a vitamin;


- a mineral;


- a herb or other botanical;


- an amino acid; a dietary substance for increasing the caloric intake;


- a combination of any ingredient described above. (3)


Whilst the marketing behind dietary supplements might occasionally adopt a medical swagger, such substances are strictly classified as foods in both the EU (4) and the United States. Indeed, amongst the DSHEA’s most important stipulations for a dietary supplement are that it must not contain an FDA-approved drug, antibiotic, or biologic, and that it must not be intended to treat or prevent disease. This is a crucial point that represents an attempt by the FDA to legislate into existence a strict boundary dividing foodstuffs from pharmaceuticals. Unfortunately, however, some substances have been found to have transgressed that boundary.




Sildenafil is the active pharmacological ingredient (API) of a number of medications used to treat erectile dysfunction and pulmonary arterial hypertension, including Viagra and Revatio. Originally discovered by Pfizer in 1989, sildenafil was approved for medical use in the United States and Europe in 1998; the drug has gone on to become the 217th most commonly prescribed medication in the USA. (5)


Pfizer’s final patents on sildenafil expired in 2017, the same year that the drug was approved for over-the-counter sale in the UK. (6) Some people may experience headaches, hot flushes, and feelings of sickness or dizziness after taking sildenafil, but such side effects are uncommon and usually mild. The drug can, however, present serious health risks to those who have recently suffered a stroke or heart attack, or who are living with a serious heart or liver problem. Additionally, people taking nitrates such as nitroglycerin to treat angina, as well as those who have low blood pressure, should avoid taking sildenafil. (7)


Like many medications, then, sildenafil is not without its risks, and should therefore only be consumed for specific medical purposes. In recent years, however, sildenafil and other pharmacological substances have been found in a number of dietary supplements: one meta-analysis by the FDA found that from 2007 to 2016, an astonishing 776 dietary supplements were identified as having been adulterated. (8) 353 such products were marketed for sexual enhancement, with sildenafil being found in 166 of these – other common adulterants included the appetite suppressor sibutramine, found in 269 out of 317 weight loss supplements, and synthetic steroids or steroid-like ingredients, found in 82 out of 92 muscle building supplements. “Active pharmaceuticals continue to be identified in dietary supplements,” the study’s authors concluded, “especially those marketed for sexual enhancement or weight loss.”


Given the degree to which the stated aims of these products lines up with the medical effects of their adulterants, this is clearly not an issue of accidental cross-contamination, but one of deliberate adulteration. As discussed, the drug ingredients in these dietary supplements – inherently illegal in food products because of their pharmacological nature – present a serious risk to consumers with underlying health conditions, or those on medication.


Science for a safer world


As the global dietary supplements industry continues to grow, the sector will inevitably attract substandard manufacturers looking to outsmart the regulatory bodies, putting consumers at risk.


In order to meet the growing demand for dietary supplement analysis, LGC has developed a new category within the PHARMASSURE proficiency testing scheme which includes sildenafil identification. Designed to assist laboratories in their quest for accurate sildenafil detection and analysis, the Sildenafil in Supplements proficiency testing scheme adds an all-important dimension to our suite of sildenafil reference standards for both pharmaceutical and public health laboratories.



Get in touch today to find out more about this exciting new proficiency testing scheme! 

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