Canada has become the first country to approve a cannabis based painkiller for multiple sclerosis (MS) patients.
The spray, Sativex, which is derived from the marijuana plant, went on sale in Canada on Monday.
It is now possible to obtain Sativex by prescription through Canadian pharmacies.
British drug company GW Pharmaceuticals, developed the drug which is marketed in Canada by Bayer HealthCare.
Health Canada, the federal agency that oversees medical care for Canadians, approved Sativex in April. Sativex is made from components derived from the cannabis plant that have been shown to ease pain.
In general the medical profession has welcomed the availability of the drug.
Dr. Allan Gordon, a neurologist and director of the Wasser Pain Management Center at Mount Sinai Hospital in Toronto, says effective pain control and management are extremely important in a disease like MS, and the availability of Sativex addresses the great demand for an effective treatment option in the field of neuropathic pain in MS.
Multiple sclerosis, is an autoimmune disease that affects the central nervous system, and many sufferers treat their pain by smoking marijuana, but the dose is hard to regulate and the drug is difficult to obtain legally.
According to the U.S. National Multiple Sclerosis Society, of the 2.5 million worldwide who are believed to have MS, about 50,000 are Canadian, and about half that number of MS patients say they suffer from chronic pain.
Sativex is administered through a spray pump under the tongue or on the inside of the cheek.
Canada, in 2001, became the first country to adopt a system regulating the medicinal use of marijuana for people suffering from terminal illnesses and chronic conditions.
In the United States, the federal government has classified marijuana as a drug that is as dangerous as heroin, nevertheless 10 states have passed laws that allow its use under medical supervision.