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Despite increased acceptance from the medical community (former U.S. Surgeon General Joycelyn Eldersclaims “the unjust prohibition of marijuana has done more damage to public health than has marijuana itself”), cannabis still carries a social stigma that has been surprisingly hard to shake. Below, CannaMD takes a look at the top research studies that have swayed some of marijuana’s biggest critics.

Editor’s Note: Today’s post was written for CannaFacts, the official Facebook group for evidence-based discussion of medical cannabis research. To stay up to date with future studies, be sure to join today!


In 2013, neurosurgeon and chief CNN Medical Correspondent, Dr. Sanjay Gupta, made headlines with a public apology for previously opposing medical marijuana:

I apologize because I didn’t look hard enough, until now. I didn’t look far enough. I didn’t review papers from smaller labs in other countries doing some remarkable research, and I was too dismissive of the loud chorus of legitimate patients whose symptoms improved on cannabis.

Gupta continued, speaking to common misconceptions concerning marijuana’s federal prohibition:

I mistakenly believed the Drug Enforcement Agency listed marijuana as a schedule one substance because of sound scientific proof. Surely, they must have quality reasoning as to why marijuana is in the category of the most dangerous drugs that have “no accepted medicinal use and a high potential for abuse.”

They didn’t have the science to support that claim, and I now know that when it comes to marijuana neither of those things are true. It doesn’t have a high potential for abuse, and there are very legitimate medical applications. In fact, sometimes marijuana is the only thing that works.

Dr. Kate Scannell, former medical director of one of the country’s first hospital AIDS wards, voices agreement:

From working with AIDS and cancer patients, I repeatedly saw how marijuana could ameliorate a patient’s debilitating fatigue, restore appetite, diminish pain, remedy nausea, cure vomiting, and curtail down-to-the-bone weight loss. The federal obsession with a political agenda that keeps marijuana out of the hands of sick and dying people is appalling and irrational.

While just the tip of the iceberg, the following studies highlight a wealth of growing research supporting Gupta, Scannell, and the countless medical professionals calling for a change in social perception.


In 2016, Pharmacotherapy published results of a retrospective chart review analyzing medical marijuana use in 121 migraine patients. The study showed marijuana successfully prevented migraines; patients who used marijuana experienced 5.8 less migraine days a month.  Moreover, patients also reported that marijuana stopped migraines in-progress.

These findings support a separate study presented at the Third Congress of the European Academy of Neurology which concluded:

Cannabinoids are just as suitable as a [means of prevention] for migraine attacks as other pharmaceutical treatments.

As lead study author Maria Nicolodi summarizes:

We were able to demonstrate that cannabinoids are an alternative to established treatments in migraine prevention.


A 2016 Frontiers in Pharmacology study found that CBD may help post traumatic stress disorder (PTSD)patients by reducing learned fear – a condition that triggers the fight or flight response at inappropriate times. Researchers think cannabis may work by decreasing fear expression, disrupting memory reconsolidation, and enhancing extinction (the process by which exposure therapy inhibits learned fear).

Researchers concluded:

A growing body of literature provides compelling evidence that CBD has anxiolytic effects and recent studies have established a role for CBD in regulating learned fear by dampening its expression, disrupting its reconsolidation, and facilitating its extinction.

Although we found no effect of CBD on auditory fear extinction, decreasing fear expression during extinction without interfering in its encoding is still a useful property that has clinical implications. In this respect CBD might be an improvement over other available drugs used for treating the fear-related symptoms of phobias and PTSD.


Research suggests cannabis may exert anti-cancer effects by causing cell death, modulating cell-signaling pathways, and inhibiting tumor invasion. For instance, a 2011 study found that CBD kills breast cancer cells by inducing endoplasmic reticulum stress and inhibiting cell-signaling. Likewise, colon cancer studies show that CBD has a cancer-protective effect and reduces cell proliferation.

Perhaps most exciting, the National Cancer Institute notes that:

Cannabinoids appear to kill tumor cells but do not affect their non-transformed counterparts and may even protect them from cell death.


A five-week double-blind, placebo-controlled study found that multiple sclerosis patients who used whole-plant cannabis-based medication (including cannabinoids THC and CBD) experienced reduced pain intensity.

The same 2005 study also found that cannabis-based medication decreased sleep disturbances, leading researchers to conclude:

Cannabis-based medicine is effective in reducing pain and sleep disturbance in patients with multiple sclerosis related central neuropathic pain and is mostly well tolerated.


In 2011, the Israel Medical Association Journal reported findings from the first ever study on cannabis use in Crohn’s disease. Conducting retrospective interviews, researchers concluded:

The results indicate that cannabis may have a positive effect on disease activity, as reflected by reduction in disease activity index and in the need for other drugs and surgery.

Perhaps of most interest, the study authors added:

The central effect of cannabinoids may induce a sensation of general well-being, which could contribute to the feeling that cannabis use is beneficial. However, this general effect wears off with time as tolerance develops, while the positive effect of cannabis on disease activity in our patients was maintained for an average period of 3.1 years.

Of the 30 study participants, 21 improved “significantly” after treatment with cannabis. The need for other medication was also “significantly reduced.”


In 2011, the American Journal of Epidemiology reviewed two population-based nationally representative studies exploring the relationship between marijuana use and obesity. After analyzing results from over 50,000 respondents, researchers concluded:

The prevalence of obesity was significantly lower in cannabis users than in nonusers […] The proportion of obese participants decreased with the frequency of cannabis use.

Addressing widely held stereotypes, the authors added:

This cross-sectional analysis indicated that despite the evidence that cannabis use stimulates appetite in clinical trials and laboratory studies, cannabis users are actually less likely to be obese than nonusers in the general population.

Likewise, a study from 2006 found that even though marijuana use may be correlated with increased caloric intake, it is not associated with higher body mass index (BMI) or glucose levels.


In addition to lower rates of obesity, cannabis users also demonstrate a lower risk for diabetes, with a recent study concluding:

In a robust multivariate model controlling for socio-demographic factors, laboratory values and comorbidity, the lower odds of diabetes mellitus among marijuana users was significant […] Marijuana use was independently associated with a lower prevalence of diabetes mellitus.

(Results were so impressive that Time followed up with an article titled, Marijuana: The Next Diabetes Drug?.)

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Speaking of his own 2013 research, Harvard Medical School professor Murray Mittleman writes:

The most important finding is that current users of marijuana appeared to have better carbohydrate metabolism than nonusers. Their fasting insulin levels were lower, and they appeared to be less resistant to the insulin produced by their body to maintain a normal blood-sugar level.


In 2004, researchers reported that THC may effectively treat ALS:

Our research indicates that select marijuana compounds, including THC, significantly slow the disease process and extend the life of mice with ALS.

In an astonishing announcement, study author Dr. Mary Abood revealed:

The only FDA approved drug for ALS, riluzole, extends life on average by about two months. Evidence from our study suggests that a marijuana-based therapy could create a much greater effect, perhaps extending life by three years or more.

Follow-up studies support Abood’s claim, with a number of journals reporting similar results:

These results show that cannabinoids have significant neuroprotective effects in this model of ALS.


In a randomized double-blind, placebo-controlled trial performed at 30 clinic centers, researchers found that the addition of CBD to traditional seizure medication significantly decreased the rate of drop (or atonic) seizures. Specifically, study results showed that in a group of 225 people, drop seizures decreased from baseline by:

  • 41.9% in the 20-mg CBD group
  • 37.2% in the 10-mg CBD group
  • 17.2% in the placebo group

Another cannabinoid, CBDV, has recently gained attention in the epilepsy community, with a 2012 mouse and rat study concluding:

The significant anticonvulsant effects and favorable motor side effect profile demonstrated in this study identify CBDV as a potential standalone anti-epileptic drug or as a clinically useful adjunctive treatment alongside other anti-epileptic drugs.


Cannabis has long been recognized as an effective treatment for HIV/AIDS symptoms and medication side effects. According to a 2004 study published by the Journal of Acquired Immune Deficiency Syndrome:

A substantial percentage of cannabis users viewed it as beneficial for relief of symptoms commonly associated with HIV/AIDS. Relief from anxiety and depression were among the most frequently reported reasons for smoking cannabis, followed by appetite stimulation and relief of nausea.

As researchers note:

This finding is particularly relevant to issues of antiretroviral medication adherence. Nausea and anorexia are frequently cited as reasons for delayed or missed doses and discontinuation of ART.

In fact, Dronabinol (Marinol), a synthetic form of THC, is approved by the Food and Drug Administration for treatment of HIV-associated loss of appetite. (For more on THC and Marinol, see the Journal of Analytical Toxicology.)


In 2014, Clinical Neuropharmacology reported that marijuana improves Parkinson’s motor symptoms including tremors, rigidity, and bradykinesia, as well as non-motor symptoms such as pain and sleep disorders. Follow-up studies appear to support these results, with a 2015 survey finding:

Cannabis was rated as the most effective therapy for sleep and mood improvement amongst all complementary and alternative medications.

Likewise, the Journal of Psychopharmacology reports:

We found significant improvements in measures of functioning and well-being of Parkinson’s disease patients treated with CBD [cannabidiol] 300 mg/day compared to a group that received placebo.

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