SACRAMENTO, California (AP) – The first US clinical trials in more than two decades on the medical benefits of marijuana confirm pot is effective in reducing muscle spasms associated with multiple sclerosis and pain caused by certain neurological injuries or illnesses, according to a report issued last week.

Igor Grant, a psychiatrist who directs the Center for Medicinal Cannabis Research at the University of California, San Diego, said the five studies funded by the state involved volunteers who were randomly given real marijuana or placebos to determine if the herb provided relief not seen from traditional medicines. "There is good evidence now that cannabinoids may be either an adjunct or a first-line treatment," Grant said at a news conference where he presented the findings.

The California Legislature established the research centre in 2000 to examine whether the therapeutic claims of medical marijuana advocates could withstand scientific scrutiny. In 1996, state voters became the first in the nation to pass a law approving pot use for medical purposes.

Thirteen other states have followed suit, but California is the only one so far to sponsor medical marijuana research. After ten years and nearly $9 million, the Center for Medicinal Cannabis Research is preparing to wrap up its work next year.

Along with the studies on muscle spasms and pain associated with spinal cord injuries and AIDS, the centre also has funded research on how marijuana effects sleep and driving, limb pain due to diabetes, and whether inhaling vaporised cannabis is as effective as smoking it. A laboratory study supported by the centre examined if pot could be helpful in treating migraine headaches and facial pain. In that study, rats given a cannabis-like drug exhibited reduced activity of nerve cells that transmit pain.

State Sen. Mark Leno, a San Francisco Democrat who chairs a budget subcommittee on health and human services and supports medical marijuana, said he doubted there would be more financial support for the centre given California's ongoing budget crisis. The federal government classifies marijuana as an illicit drug with no medical use but produces the only pot legally available for scientific research under a contract with the University of Mississippi.

Grant said obtaining some of the Mississippi crop and meeting the complex security regulations required by the Drug Enforcement Agency and other federal agencies was time-consuming and cumbersome.

Grant, however, had no problem with the quality of the government's supply. Its consistency was helpful in determining that patients who smoked less-potent marijuana enjoyed the same amount of pain relief but less mental confusion than those who inhaled a more powerful strain, he said.