The reality is that marijuana鈥檚 designation as an illegal substance has really limited the amount of research done on the subject and most claims simply have no evidence one way or the other.
One of the most comprehensive review articles on the subject of medial marijuana and a subsequent report by the National Academies of Science Engineering and Medicine found that the evidence is fairly thin all around. There is evidence in support of the idea that marijuana can help with chronic pain (with most studies being on nerve pain) and help with the nausea caused by chemotherapy. There was also evidence that it can help with spasticity in patients with multiple sclerosis.
The quality of the evidence is debatable since many trials looked not at smoked marijuana but at oral cannabinoids (medications that contain one or a mixture of the active ingredients from the marijuana plant. Also, not all studies have used a placebo group and fewer still compared marijuana or oral cannabinoids to other treatments already on the market.
Very recently, a study showed that an oral cannabidiol solution could be used as a treatment in Dravet syndrome, a rare genetic form of epilepsy in children. This result may not apply to smoked marijuana where the levels of THC might negate the positive effects and also might not apply to all forms of epilepsy. Nevertheless, this study was a good demonstration of how the active ingredient in the marijuana plant can be used to develop a new medication for a difficult to treat condition. What this means for marijuana smoking is more difficult to judge.
Of the many other claims, the evidence is scant. There is some limited quality evidence that it can help stimulate appetite and weight gain in HIV patients and some evidence that it may help with sleep and suppress tics in patients with Tourette鈥檚 Syndrome although this is based mainly on small studies with few patients. Interestingly enough, even though this claim is often repeated, there is actually no good evidence that marijuana can help with glaucoma.
The problem with any discussion regarding medical marijuana is that the hype tends to outpace the evidence. People will take the fairly limited claim that marijuana can be used to treat nausea caused by chemotherapy, and then expand it to say that marijuana can be used to treat cancer, which is not at all true.
As with all medications, marijuana has some benefits, some side effects, and some uncertainty regarding its use. Some studies suggest that marijuana (especially smoked marijuana) has negative effects on both the heart and lungs.
The real take away message, though, is that we need more data. We need more studies to say definitively where it might help, but also to clearly say where it won鈥檛.
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