Marijuana provides greater pain relief when taken in pill form than when it is smoked, according to a study that touches on a controversial medical issue.
Cancer and multiple sclerosis doctors are looking more and more closely at cannabis for patients seeking relief from pain, and some jurisdictions allow the medical use of the drug for this purpose.
But marijuana smoke also carries health risks, for it carries carcinogens and respiratory irritants and users tend to inhale deeply and hold their breath to gain maximum effect.
Neuroscientists in the United States have now carried out what they say is the first scientific study to compare pain relief between smoked marijuana and pills with tetrahydrocannabinol, or THC, which is the active ingredient in the drug.
A team led by Ziva Cooper and Margaret Haney of Columbia University in New York asked 15 male and 15 female volunteers, all of them daily cannabis smokers, to carry out a pain test after having smoked marijuana, taken a pill or a dummy look-a-like called a placebo.
The experiment entailed a "cold pressor test", in which the participants immersed a hand into a bath of extremely cold water for up to two minutes, during which they reported on the sensation of pain.
Both smoked marijuana and the THC decreased pain sensitivity and boosted tolerance to pain compared to the placebo.
But the pill beat marijuana for long-lasting decreases in pain.
The findings are promising for medical uses of the THC pill, but more work is needed to determine its impact on individuals who do not smoke marijuana, say the investigators.
The study appears in the journal Neuropsychopharmacology.