It says that for some seriously ill people, the benefits outweigh its disadvantages.

The Institute of Medicine (IOM) report, commissioned by the White House Office of National Drug Control Policy, states that marijuana is not particularly addictive and that there is no conclusive evidence that it leads to the use of hard drugs like heroin.

The report comes on the back of a similar study in the UK by the House of Lords, which supported the medicinal use of cannabis.

Two UK trials were launched in January for patients with multiple sclerosis and post-operative pain.

The US report looked at patient experience as well as scientific evidence.

Its authors expressed concern about the risks related to smoking cannabis.

But it said: "Nonetheless, for certain patients such as the terminally ill or those with debilitating symptoms, the long-term risks are not of great concern."

Multiple sclerosis

Campaigners for the legalisation of cannabis say the drug can relieve the aches and pains associated with conditions such as multiple sclerosis and Aids.

It can also help relieve symptoms of anxiety, lack of appetite and nausea.

The report calls for more research into the development of safer ways of delivering cannabinoid drugs - the active ingredient of marijuana - which act as quickly as cigarettes.

Cannabis can relieve the symptoms of some chronic and terminal illnesses

In their response to the House of Lords, British doctors also stressed the need for the development of non-smokeable cannabinoid drugs.

However, the US report recognises that many chronically ill patients may not want to wait for the outcome of research.

"We acknowledge that there is no clear alternative for people suffering from chronic conditions that might be relieved by smoking marijuana such as pain or Aids wasting," it stated.

Its authors called for these patients to be allowed to be involved in clinical studies of marijuana's medicinal effects, with the risks and rewards of smoking the drug being carefully explained to them.

Heated debate

The issue of medicinal use of cannabis has provoked a heated debate in the US.

Last autumn, the House of Congress voted by 310 to 93 not to legalise marijuana for medicinal use.

The IOM report was commissioned in 1997 by Barry McCaffrey, President Clinton's anti-drugs czar, who is opposed to relaxing laws on legalising cannabis.

He had hoped it would give a scientific basis to the discussion over medicinal use.

Several US states have recently legalised cannabis for severely ill patients.

The first was California in 1996, but its decision was blocked by the federal government.

However, last year, six other states voted for similar measures, increasing pressure on the federal government to move cannabis from the dangerous drug list.

Mr McCaffrey's office said it would study the report carefully.

"We look forward to the considered responses from our nation's public health officials to the interim solutions recommended by the report."

But campaigners for the legalisation of cannabis said the report backed their stance.