Why cannabis studies contradict each other

Studies on cannabis are both numerous and still rare. And when they are published, they sometimes tend to contradict one another. Why? American scientists complain about the’restricted access to cannabis, the lack of infrastructure and resources to study the benefits and risks of this plant.

No large-scale testing

Several factors may account for the conflicting conclusions of studies on medical cannabis. First, the product’s illegal status. Scientists have difficulty accessing medical cannabis. Whether in France or the United States, the administrative process is lengthy, and legal sources of supply are scarce. When samples finally arrive, with often low-quality weed, and since they do not reflect the products found on the street either, the test panels are often too small to be completely reliable.

Aditi Kalla, from the Einstein Medical Center, sums it up well: «There isn’t adequate infrastructure to study cannabis properly. But whether people say good or bad things about it, we just want to guide future research.»

Example of a contradiction

One of the many issues being studied in relation to cannabis is the possible increase in the risk of cardiovascular events. A massive study of 20 million medical records—including 316,000 cannabis users—found a 10% increase in stroke risk. The problem is that an international study followed 5,000 people for 20 years. Scientists have concluded that there is no link between cardiovascular events and marijuana use. Another from Sweden is consistent with the latter. And these are just three among hundreds. It is therefore difficult to form a clear-cut and definitive opinion on the matter.

Since the substance is banned, scientists must also rely on patients to be truthful about their use of the substance, their lifestyle, and their consumption of legal drugs.

And even as its use becomes more widespread and people become more open about it, the politicization of cannabis is causing unease in the scientific community, which is often divided on the ultimate outcome of medical cannabis use.

Where the studies agree

Some studies do, however, agree. It is verified today that medical cannabis can relieve chronic pain and nausea in cancer patients and help manage spasticity associated with multiple sclerosis. For some individuals, however, cannabis use results in harmful side effects—both short-term and long-term—that science has yet to fully understand.