People who order prescription drugs over the internet are playing 'Russion roulette' with their health, the Trading Standards Institute have warned.
Pills bought from foreign websites could be contaminated fakes and misuse or excessive doses could have serious and even fatal health consequences, the TSI said.
Its warnings are based on sample purchases of Viagra, Tamiflu, Prozac and Valium from foreign websites by trading standards officers.
Some of the 20 drugs ordered online arrived with no instructions for use. Three of them came with no supplier or manufacturer information. Others failed to turn up at all.
Oxfordshire trading standards officers ordered 10 prescription-only drugs from websites based in countries such as Canada, Panama and India. Fertility drug Clomid and Diazepam, also known as Valium, both arrived in Jiffy bags with no instructions, warnings or dosage directions.
Other samples of Viagra, Tamiflu, Prozac and Valium appeared to be genuine. One £54 order for 10 Viagra tablets failed to turn up six weeks after the money had been paid.
TSI chairman Nigel Strick said taking drugs without a prescription could be extremely dangerous: "We warn people that it is most inadvisable to seek to obtain such drugs without proper medical guidance and a prescription. They are playing a dangerous game of Russian roulette if they do," he said.
"And, beyond that very real danger, there is also the risk that the drugs ordered in this way may not arrive at all or could be counterfeit - and it would be extremely difficult to get your money back from a seller based abroad."
Mick Deats, head of enforcement and intelligence at the Medicines and Healthcare Products Regulatory Agency (MHRA), said the sale and supply of counterfeit medicines is on the increase.
"Criminal gangs are targeting consumers via the internet, in pubs and clubs and through illegal advertising," he warned.
The majority of fake medicines are "lifestyle" drugs which claim to treat conditions such as hair loss, weight problems and erectile dysfunction, Mr Deats said.
The sale of medicines in the UK is regulated by the Medicines Act 1968, but overseas suppliers are not subject to these controls.
Dr Jim Kennedy, chair of the RCGP's prescribing group, said: "Customers who buy prescription drugs via the internet have no protection or comeback if they are dealing with companies based in countries which do not have legal agreements with the UK."
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