"You don't get what you think you're getting," said Monika Johansson, laboratory department manager of the Medical Products Agency (Läkemedelsverket), to newspaper Aftonbladet.
6,500 erectile dysfunction medications of 51 separate brands were confiscated in September of last year, in a joint bust conducted by Swedish police, customs officials and the Medical Products Agency.
Several of these were shown to hold low quality indeed.
The contents of 17 of the 51 analysed products differed from the specification.
Only half of the pills contained sildenafil, the active ingredient in Viagra, and medically approved in Sweden.
Several of the products contained a lower dosage of the ingredient than specified, and others were shown to contain dosages far higher than the daily maximum - a dangerous excess, risking strokes and heart problems.
Several of the products also contained unlisted active ingredients, for instance the painkiller diklofenak.
"You risk getting a useless drug. The products we've analysed contain several unlisted ingredients and are overall very poor quality," said Johansson to Aftonbladet.
The ayurvedic aphrodisiac Penisole turned out to contain the poison strychnine, which can be deadly. Strychnine has been used as a rat poison, but is prohibited in Sweden since the 1970s.
"Naturally it's worrying that this substance was found in products that just about anyone can buy. In this particular product it was a low dosage, which won't cause any symptoms," said Mark Personne, chief of medicine at the Swedish Poisons Information Centre (Giftinformationscentralen), to Aftonbladet.
The Medical Products Agency has now issued a warning against these products, urging the public not to buy any medication against erectile dysfunction on unknown Internet sites.