Multinational drug companies are showering doctors in the developing world with gifts and inducements to persuade them to prescribe drugs of dubious value, an investigation has revealed.

Intense marketing of medicines has resulted in up to half of drugs being wrongly prescribed, the campaign group Consumers International says in its report Drugs, Doctors and Dinners. It calls for a ban on gifts to doctors.

A GP in Malaysia, Rafik Ibrahim, who practises near the capital, Kuala Lumpur, described how in a period of five weeks in August last year he spent 17 hours with drug-sales representatives who approached him on behalf of 25 drug companies. In Pakistan, doctors who wrote 200 prescriptions for one high-price drug were offered the down payment on a new car.

Multinational companies are turning to the developing world as profits stagnate in the West. But regulation in these countries is weak and drug sales representatives can influence prescribing by the inducements they offer.

India was one of the fastest-growing markets last year, with sales increasing 17.5 per cent to $7.3bn. But the health commission, in 2005, labelled 10 out of the 25 top-selling medicines as being "irrational or non-essential or hazardous".

Richard Lloyd, of Consumers International, said: "The pharma industry sees the developing world as a trillion-dollar opportunity... but consumer health expenditure in these countries can ill afford to be squandered." He added: "The best way to ensure patients in the developing world get rational impartial treatment is... to ban gifts for doctors."