"Illegal Internet pharmacies have started to use social media to get customers for their websites," Hamid Ghodse, president of the International Narcotics Control Board, said in the agency's annual report published Tuesday.
This "can put large, and especially young, audiences at risk of dangerous products, given that the World Health Organisation has found that over half of the medicines from illegal Internet pharmacies are counterfeit," he said.
Illegal online pharmacies often pretend to be legal but in fact smuggle illicit products to their customers, the INCB found, urging governments to close them down.
More broadly, the agency called for greater efforts to tackle poverty, violence, organised crime and corruption as these created a climate for drug abuse and trafficking, with young people among the biggest victims.
"Youth of these communities must have similar chances to those in the wider society and have a right to be protected from drug abuse and drug dependence," said Ghodse.