More than 5,000 unlicensed slimming pills were seized from a wardrobe following a raid at a Preston home.
Police and experts from the Medicines and Healthcare Products Regulatory Agency (MHRA) raided an address in Frenchwood, and found drugs worth about £14,000 in an upstairs bedroom.
The operation was part of an £8.6m seizure of counterfeit and unlicensed medicines in the UK, within an international crackdown on the illegal internet trade of medicines.
Officers raided the terraced home in Roman Road, and found about 5,200 Sibutril tablets, which are unlicensed slimming pills.
They are believed to contain Sibutramine, which was banned in the UK and Europe in 2010 because of an increased risk of heart attack and stroke.
Danny Lee-Frost, head of operations, said the MHRA was investigating the importation of unlicensed medicines coming into the UK.
He said: “The objective is to get the message out that the internet is not safe to buy medicines.”
He added: “You don’t know what you’re getting, where it’s come from or who has been dealing with it, especially if you are receiving just the blister pack.”
A 36-year-old man was arrested on suspicion of obtaining services by deception, in connection with the probe.
It is alleged that he used forged documents to open mail box facilities.
He was bailed by police until August pending further investigation.
The operation was part of Operation Pangea VII, which seized huge hauls of potentially harmful slimming pills and controlled drugs such as diazepam and anabolic steroids.
The international crackdown resulted in seizures totalling about £18.6m worldwide.
In the UK, the operation resulted in the seizure of 3.6 million doses of counterfeit and unlicensed medicines, five arrests and the shutdown of 1,891 websites.
The MHRA’s head of enforcement, Alastair Jeffrey, said: “Operation Pangea is the global response to internet facilitated medicines crime.
“During a week of action we have seized £8.6 million worth of counterfeit and unlicensed medicines, shut down 1,891 websites operating illegally and removed nearly 20,000 links to these sites that were supported by social media platforms.”
For video, see lep.co.uk.