Canadian health authorities have given approval for a new cannabis-based painkiller for use with cancer patients.
The drug Sativex, is sprayed it into the mouth and helps alleviate the pain of cancer sufferers.
The drug is for use in cancer patients who suffer from neuropathic or nerve pain, which is excruciating and difficult to control and is meant as an adjunctive treatment, which can be used alongside other drugs such as morphine.
Experts say it will be another way to reduce pain and will be particularly helpful for people with advanced cancer who experience significant pain for which there are few pain-relief options currently available.
Sativex contains the active ingredients that give pot smokers their high, including delta-9-tetrahydrocannabinol (THC) and cannabidiol (CBD).
For cancer sufferers the drug will provides relief from severe pain rather than pleasure, in much the same way opium and heroin are used medicinally.
Each spray delivers a fixed dose of 2.7 milligrams of THC and 2.5 mg of CBD with patients able to control the number of doses; it is recommended they not exceed 14 sprays daily.
The drug is expensive and costs around $125 per vial; each vial contains 51 sprays and the average daily dose is five sprays, which equates to an average cost of about $12.25 a day.
The prescription drug is covered by most private insurance plans, but not as yet by any provincial drug plans.
Canada was the first country in the world to approve the sale of a prescription painkiller derived from cannabis in 2005 and initially allowed Sativex on the market for the treatment of the severe pain associated with multiple sclerosis.
It belongs to a class of drugs known as cannabinoids which includes Rimonabant, a high-profile anti-obesity drug from Sanofi-Aventis, and Marinol and Cesamet, drugs used to treat nausea and vomiting in cancer patients undergoing chemotherapy.
Cannabinoids are causing quite a stir in scientific circles because there are 10 times as many cannabinoid receptors in the brain as opioid receptors, meaning the drugs should be more effective at blocking pain.
Sativex is believed to act via cannabinoid receptors that are distributed throughout the central nervous system and in immune cells; they are distributed throughout the pain pathways of the nervous system, and their activation is known to reduce pain.
Cannabinoids also appear to have fewer side effects than those derived from opium though some users of Sativex have complained the spray leaves an odd after taste and can cause minor gastrointestinal problems.
Codeine and morphine can cause severe constipation and drowsiness and opioids are highly addictive.