The operation, codenamed Pangea, involved dozens of locations in Britain, Germany, Ireland, Israel, New Zealand, Singapore, Switzerland, Canada and the US.
Sales of medicines via the web are a growing problem, since many of the products are counterfeits of dubious quality and potentially dangerous.
Britain's Medicines and Healthcare products Regulatory Agency, which raided 12 residential and commercial premises in the crackdown, said illegal Internet sales posed a serious risk to public health, according to Reuters.
The Vienna-based International Narcotics Control Board says that in many countries, the abuse and trafficking of prescription drugs now equals or exceeds the use of illicitly manufactured heroin, cocaine, amphetamine and opioids.
In Britain, operation Pangea resulted in the seizure of computers, documents and more than a thousand packs of unlicensed medicines.
Products seized including drugs claiming to treat conditions such as diabetes, impotency, obesity, hair loss and male breast growth as a side effect from bodybuilding steroid abuse.
The Internet provides an easy channel because there are no national control mechanisms.
Properly regulated, Internet pharmacies can provide a valuable service by increasing competition and offering access to treatments in underserved areas.
But the online world is also a Wild West of spam e-mails and hard-to-trace suppliers, according to healthcare regulators.
(Editing by Giles Elgood)