Cannabis has a long history as a pain-reliever 鈥� it is . But there is still active debate over the extent of the drug鈥檚 analgesic properties.
On the one hand, there is some evidence that cannabis can relieve certain types of pain. For instance, in a small trial published about 15 years ago, researchers found the drug could reduce the pain associated with an injection of capsaicin, a compound in chilli peppers that induces a sensation of burning 鈥� although there was an unusual relationship between drug dose and pain relief.
The science of cannabis
As the use of marijuana and its compounds rises around the world, New 杏吧原创 explores the latest research on the medical potential of cannabis, how it is grown and its environmental impact, the way cannabis affects our bodies and minds and what the marijuana of the future will look like.
Men who smoked cannabis containing a 鈥渕edium鈥� dose of 4 per cent tetrahydrocannabinol (THC) by weight reported feeling relatively little pain when they were then injected with capsaicin. But men who had smoked cannabis containing a 鈥渉igh鈥� dose of 8 per cent THC by weight .
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A more recent study, from 2015, also found pain-relieving benefits. Among 15 volunteers, , with the degree of pain relief increasing alongside the increasing THC doses.
But cannabis may be ineffective for relieving some other forms of pain. For instance, a small study in women from 2008 found that . Indeed, the THC actually reduced the amount of electrical pain the women could tolerate at the affected area.
鈥淚鈥檓 not convinced by cannabis鈥� [pain] efficacy because of a lack of high-quality randomised controlled trials (RCTs), our gold standard form of study,鈥� says at the University of Sydney in Australia. 鈥淢ost studies are at a high risk of bias and of a low quality.鈥�
To try to address concerns like this, in 2018 a group of researchers published a review of 104 studies, including 47 RCTs. These studies looked into the effects of cannabinoids 鈥� a class of chemicals in cannabis that includes THC 鈥� on chronic non-cancer pain. The review concluded that , but this falls away when the bar is upped to 50 per cent.
Even if cannabis does have some pain-relieving properties, it is still not completely clear how it achieves this.
Based on the research to date, THC appears to be the main pain-relieving player. By binding tightly to the receptor CB1, , it modulates the release of chemical messengers, or neurotransmitters. THC also binds to a different receptor 鈥� CB2 鈥� which largely resides in immune cells, keeping them in check to manage inflammation. Through CB1 and CB2 binding, THC regulates neurotransmitters involved in pain and dampens inflammation.
But there are other cannabinoid that might play a part in relieving pain too. One is cannabidiol, better known as CBD. It is often sold as an oil, spray or gummies for sleep or stress. Structurally similar to THC but lacking its psychoactive properties, , a study in rats suggests. And cannabinoids don鈥檛 stop with THC and CBD 鈥� , to name a few, may also provide some pain relief, however big or small.
It is possible that cannabis鈥檚 pain-relieving properties may involve additional pathways. Cannabinoids also bind to and to the , which plays a role in pain. Cannabinoids鈥� may also extend to other cannabis compounds, such as flavonoids.
Whatever the mode 鈥� or modes 鈥� of pain-relief action, there is also evidence that regular cannabis users may actually go on to experience more severe discomfort. In a study published earlier this year, researchers had people immerse their hand in icy water for as long as they could stand it. , on average, surpassing the 26 seconds of those who regularly used both cannabis and tobacco, but falling far behind the 105 seconds of those who used neither drug.
鈥淎nything that instantly reduces your pain, if you take it long term, the brain overshoots,鈥� says at Upstate University Hospital in New York. Pain is thought to have evolved so that we take action to stop or limit any damage. With cannabis, 鈥渢he pain drivers overcompensate, as if the brain is saying 鈥榞ee, we really need to feel pain鈥欌��, says Johnson. 鈥淚f you use marijuana frequently, you might feel more pain long term.鈥�
With questions remaining over cannabis鈥� pain-relieving potential, and the mechanisms behind it, Wilson says the drug shouldn鈥檛 be seen as a 鈥減anacea鈥�. Cannabis can be used legally to relieve pain in many countries, with the UK, Australia and parts of the US permitting the drug for medical use.
鈥淚f you find marijuana helpful and you use it once and a while, that鈥檚 fine, but using a short-acting drug [such as cannabis] constantly, that鈥檚 when you ramp up your pain system,鈥� says Johnson.
