The MHRA seized £570,000 worth of illicit and counterfeit pills between October 5 and 12, as part of an international operation targeting the online sale of counterfeit and illegal medicines.
Premises linked to 12 websites were raided across the country, the MHRA said.
Medicines seized included those for erectile dysfunction, weight loss, pain relief, human growth hormone, anti-depressants and steroids.
The Metropolitan Police Central e-Crime Unit are currently working with internet service providers to close down a further 183 websites.
Forty-five countries across the globe took part in the international enforcement Operation Pangea III which resulted in 76 people being arrested or placed under investigation across the globe. Internet monitoring revealed 694 websites potentially engaged in illegal activity including offering controlled or prescription only drugs globally.