The Medicines and Healthcare products Regulatory Agency (MHRA) says it has seized a record £12.2 million of fake and unlicensed medicines in the UK as part of a week long international crack down.
They say a large amount of these were unlicensed diet pills which often contain harmful ingredients.
"What we're seeing is people going online, self diagnosing and self prescribing," said Danny Lee Frost, from the agency.
Newsbeat's Greg Dawson reports.
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