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If you were to search for a product called “Mens Maximum Energy Supplement" on Amazon, you'd be bombarded with everything from caffeine pills to amino acid supplements to the latest herb craze. But at some point last year, the FDA had purchased a specific product by that name from Amazon and sent it off to one of its labs to find out if the self-proclaimed "dietary supplement" contained anything that would actually boost energy.

In August, the FDA announced that the supposed supplement was actually a vehicle for a prescription drug that offered a very specific type of energy boost. It contained sildenafil, a drug much better known by its brand name: Viagra.

Four months later, the FDA is finally getting around to issuing a warning letter to Amazon, giving it 15 days to not only address Mens Maximum Energy Supplement and a handful of similar vehicles for prescription erection boosters, but also asking for an explanation of how the company is going to keep similarly mislabelled prescription drugs from being hawked on its site in the future.