Erectile dysfunction supplements being sold online have little to no science to prove they work, experts have warned.
A study of 21 ingredients used in six of Amazon's most highly rated erection supplements in the US found most had never even been tested in a study.
Only four ingredients had ever been proven to help and, while each pill contained at least one of those four, they also contained many other unproven ones.
The research also found a vast majority of positive reviews may not have been from genuine customers.
Scientists said people should be wary of being swayed by positive reviews or marketing and may be better off with medical options like Viagra.
Six erectile dysfunction supplements for sale on Amazon in the US were found to contain a total of 17 active ingredients for which experts couldn't find any scientific evidence to prove they would help a man with erection difficulties
The research by the Baylor College of Medicine in Texas looked at six of the most popular supplements on Amazon in September 2018.
The products were Korean Panax Ginseng (by NutraChamps), Leyzene with Royal Jelly (Natural Subsistence), Horny Goat Weed Extract (Zhou Nutrition), Boost Elite (Zhou Nutrition), Extra Strength L Arginine (Havasu Nutrition), and IncrediBULL (eSupplements).
They contained four ingredients which studies suggest could actually improve the strength and frequency of a man's erections were ginseng, l-arginine, tribulus terrestris and maca root.
But the supplements also contained 17 other 'active' ingredients which science has never proved could improve erections, the research showed.
These included tongkat ali, horny goat weed, muira puama, capsicum annuum, zinc, epimedium, saw palmetto berry, fenugreek seed and yohimbe bark.
Diindolylmethane, AAKG, piperine, gluconolactone, L-citrulline malate, polypodium vulgare, rehmania root and royal jelly all also had no science to suggest they work.
Researchers trawled a database of past scientific studies of any of these ingredients' effects on erectile dysfunction, taking in 413 studies in total – 69 on humans.
Research in the Journal of Sexual Medicine revealed many ingredients contained in supplements which claim to improve men's erections have no scientific evidence to prove they work.
Here is a list of each ingredient
