Production and sale of counterfeit drugs is on the rise in rich and poor countries, with more unwary consumers buying them over the Internet, said experts from World Health Organization (WHO).

Fake or substandard versions of medicines are often hidden in cargos taking circuitous routes to mask their country of origin as part of criminal activity worth billions.

In wealthy countries, counterfeiting often involves expensive hormones, steroids and anti-cancer medicines and pharmaceuticals related to lifestyle. But in developing countries, especially Africa, counterfeit medicines are commonly available to treat life-threatening conditions such as malaria, tuberculosis and HIV/AIDS.

Margaret Chan, WHO director-general, said that illicit products had also increased the problem of drug resistance, which is emerging as a big problem reducing the efficacy of vital anti-malarials and HIV/AIDS drugs.

Major generic drug makers India and Brazil, backed by health activists, charge that concerns about counterfeit drugs are being led by pharmaceutical companies keen to protect their patents against legitimate generic competitors.