Market researchers surveyed 205 GPs for a campaign involving the MHRA and the Royal Pharmaceutical Society of Great Britain.
They found that 57% of GPs thought that patients purchase prescription-only medicines online because they are too embarrassed to go to a GP for a prescription.
Almost all (97%) of the GPs surveyed said they thought patients use the internet to purchase medicines for erectile dysfunction.
Earlier this year, GP newspaper revealed that one in four GPs had treated patients for adverse reactions to medicines bought online.