Dangerous counterfeit and unlicensed medicines worth nearly £16m have been seized in a record haul by the UK's Medicines and Healthcare products Regulatory Agency (MHRA).
Slimming pills, drugs for erectile dysfunction and cancer medicines were taken in a series of raids.
The MHRA said criminals were making money at the expense of people's health and it was a growing problem.
Nearly 1,400 websites were closed as part of the operation.
Seven suspects are now under investigation.
The seizures were part of Operation Pangea - an international clampdown on the illegal trade in fake medicines by 115 countries.
In the UK, 6.2 million doses or medical devices were seized, worth £15.8m. Internationally, £51.6m of goods were taken.
Items seized in the UK included:
- two million doses of erectile dysfunction drugs
- slimming drugs - some of which can increase the risk of heart attacks and strokes
- narcolepsy pills
- abortion pills
- diabetes medication
- hair-loss drugs
- cancer medicines, particularly for breast and prostate
- medical devices, including fake condoms and dental laboratories
"It's amazing to me that people will buy those types of medicines over the internet," said the MHRA's head of enforcement, Alastair Jeffrey.
The drugs are not always used for their medical purposes.
Breast cancer drugs are used by some body builders to reduce their breast tissue, for example.
Many packs of narcolepsy pills were seized en route to universities, where students take them for "cognitive enhancement" - to stay awake around exam time.
Mr Jeffrey added: "Criminals involved in the illegal supply of medical products through the internet aren't interested in your health, they are interested in your money and are able to get this by selling you a potentially dangerous product or by stealing your bank details.
"To protect your health, visit your GP, get a correct diagnosis and buy medicines from a legitimate High Street or registered pharmacy which can trade online."
It is thought that people buying the drugs are made up of those who think they are buying genuine drugs and those who are getting hold of drugs a doctor would never prescribe.
The "vast majority" of the drugs came from India and China - neither country was involved in Operation Pangea.
It is unclear what the total size of the illegal drugs market in the UK is.
The MHRA said counterfeit medicines were the greatest source of profit "across the whole criminal spectrum" but insisted the UK was "way ahead of the game".
Mr Jeffrey said criminal gangs were moving into the field because, compared with illegal narcotics, sentencing was low.
"It's two years, it's not a police priority, you can use the internet as a facilitator, the risk is low and the profits are very high," he said.
He added there were "some indications" that terrorist groups were involved in "pharmaceutical crime" in the Middle East.