The Netherlands yesterday became the first country to legalise the medical use of cannabis, allowing doctors to prescribe the narcotic as a painkiller for those who are seriously ill.

In a move that is certain to put pressure on other countries to follow suit, chemists began selling the drug for a price of between €40 and €50 (£27 to £33) for a 5g (0.18oz) bag.

Although that is approximately twice the cost of buying the drug in one of the country's 1,500 coffee shops, the government claimed that there was a huge difference in quality.

It also said that the costs incurred by patients may be reimbursed by public health insurers.

Medicinal cannabis - which will be sold in the form of dried marijuana flowers from the hemp plant - is being grown to order by two official suppliers, it added, and rigorously tested for impurities.

It will be prescribed as a painkiller for people suffering from cancer, Aids, multiple sclerosis or Tourette's syndrome, but only if more conventional drugs have failed or caused unwanted side effects.

The health ministry estimates that up to 7,000 people in the Netherlands already regularly use cannabis for medical reasons and believes that the number could double once the new scheme takes off.

"Cannabis has a beneficial effect for many patients," it said in a statement.

Analysts said that Britain and parts of the United States, Australia and Canada were all considering following suit, and they would be carefully monitoring the Dutch experience.

The Dutch government is keen, however, to dispel the image of spliff-wielding patients.

It is recommending that the drug be diluted and used to make marijuana tea or administered in a special spray mechanism.

Nor is the move without controversy.

Although the drug is widely credited as an effective painkiller, some doctors argue that it increases the risk of depression and schizophrenia.