Marijuana and Alzheimer’s: What Does the Science Say?

The legalization of marijuana, whether for medical or recreational use, has been the subject of a lot of recent debate. In states where it is legal, many doctors prescribe cannabis to treat a variety of ailments including multiple sclerosis, chronic pain, and severe nausea from chemotherapy. Additionally, several studies (such as this one) have suggested that the drug’s primary active ingredient, THC, may also be useful in treating the harmful inflammation associated with Alzheimer’s disease.

The Endocannabinoid System

The reason that marijuana and other cannabinoids can get you high is because of their chemical similarity to a family of molecules produced in our own bodies called endocannabinoids. Endocannabinoids are a vital part of the brain’s signaling network and help to modulate multiple sensations including mood, pain, and hunger. THC is chemically similar to our endocannabinoids and can bind to their receptors, resulting in overactivation of the endocannabinoid system. This leads to a variety of effects including reduced focus, poor coordination, and a pleasant “high.”

Endocannabinoids and natural or synthetic cannabinoids all activate the same receptors in the brain. Image Source

Interestingly, the endocannabinoid system seems to become less active during aging. Aged rats have fewer endocannabinoid receptors present on their neurons in multiple brain regions including the hippocampus, which is considered the brain’s memory center. Unfortunately there has been little research on whether the endocannabinoid system is further disrupted by Alzheimer’s disease. The few studies that have been attempted on this topic have yielded conflicting results, and more research is needed to tease out the answer. One intriguing hint comes from a study that used a drug to increase endocannabinoid levels in the brains of Alzheimer’s mice. These mice had reduced cellular damage and memory impairment, suggesting that kickstarting the endocannabinoid system could be beneficial for neurodegeneration.

THC as an Alzheimer’s Treatment

Though our understanding of the endocannabinoid system remains poor, multiple studies have suggested that cannabinoid drugs could be a feasible treatment for Alzheimer’s disease. In one study, a group of mice with a mutation simulating Alzheimer’s disease were treated with several types of synthetic cannabinoids. This resulted in reduced inflammation and improved cognitive function. Other studies have utilized cannabidiol, a component of marijuana that does not produce any psychoactive effects, with similarly encouraging results.

Apart from the tentative successes of synthetic cannabinoids, THC has also shown some potential as an Alzheimer’s treatment. Acetylcholinesterase inhibitors, the only class of Alzheimer’s drugs currently available, were shown to be less effective than THC at preventing toxic plaque buildup in the brain. Another study found that a mixture of THC and cannabidiol was successful at improving Alzheimer’s disease in rats.

Acetylcholinesterase breaks down acetylcholine in the brain. Alzheimer’s drugs inhibit this process to improve memory. However, THC may be even more effective than our current drugs. Image Source

Safety and Efficacy in Humans

Even fewer studies have examined the effects of cannabinoids in humans. The best we have to go on so far is a few small clinical trials comprising 60 subjects in total. A synthetic version of THC called dronabinol was shown to significantly improve behavioral symptoms for many of the Alzheimer’s patients. Some side effects were reported (including tiredness and delirium) but none were severe enough to cause patients to withdraw from the trials.

Despite these encouraging results, a review paper on this topic pointed out several problems with these clinical trials. In addition to the very small sample size, many of the trials were not randomized and included only a short treatment period of between two and seven weeks. These complications make it difficult to draw conclusions from these results.

What’s the Verdict?

Unfortunately, there is simply not enough data yet to determine the safety and effectiveness of marijuana or other cannabinoids to treat Alzheimer’s disease. Based on the promising results that I described above, the topic certainly warrants further study. We can only hope that policy-makers will see past their fear of illicit drugs to provide funding for research into cannabinoids’ effects on the brain.

Related article: Cannabinoids May Combat Inflammation in Alzheimer’s

Further reading: Cannabinoids in late-onset Alzheimer’s disease

 

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