You know the one stoner friend in your group that always makes you wonder – does cannabis kill brain cells?

In this article we’ll go through the data behind whether smoking weed could cause damage to your brain and how likely it is. We’ll have a look at the latest research of cell and animal studies and assess if cannabis can lead to cell death.

If you’re interested in more information on this topic, check out JRE episode #1246 with Alex Berenson and Dr Michael Hart. I’ve also written an article on whether cannabis can cause psychosis? The quick answer is that it might.

Disclaimer: The content was created for informational purposes and is not intended to be a substitute for professional medical advice, diagnosis, or treatment.

Content:

How does cannabis work?

Simply put, cannabis contains cannabinoids, like Δ9-Tetrahydrocannabinol (THC). THC looks a lot like molecules produced by our brain, called endocannabinoids (eCBs), and can therefore perform the same functions.

THC acts on neurons in multiple areas of the brain, which have receptors for cannabinoids. These areas are responsible for things like emotions, appetite, and memory.

The main brain areas affected by cannabis consumption

To make a long story short, THC, or the body’s own endocannabinoids, are able to stop signals between certain neurons in those areas, thus interrupting communication. This leads to the effects of marijuana, like increased appetite and decreased motor control.

Endocannabinoids (eCBs) have many ways to influence neuron firing. One major one is as a circuit breaker: When eCBs (green dots) are released into the synapse, their receptor (green squiggly line) recognises them and stops oncoming neurotransmitters in neurons. Thus, the neuron (red) stops firing.

Neurons form an unimaginably vast network able to send information from one cell to the next using neurotransmitters. Scientists estimate the connections between neurons, called synapses, to be in the trillions.

Endocannabinoids (which THC mimics) were initially thought to be mere ‘circuit breakers’ – they would desensitise neurons and stop them from firing. As a result, parts of the brain expressing endocannabinoid receptors would behave differently. By decreasing excitability, eCBs have great therapeutic value, for example in the treatment of seizures.

In recent years, a more complex role for eCBs has emerged: After being thought to be present exclusively at a pre-synaptic location, receptors for eCBs have been found on nearby astrocytes (another type of brain cell) and in the main body of the neuron (somatodendritic). This allows for a much more nuanced regulation.

Does cannabis kill brain cells in a Petri dish?

Oftentimes, research starts in a simplified form – like growing one type of cell in a plastic dish, also called in vitro. This is exactly what researchers did with rat neurons. They added THC concentrations, similar to the ones found in human plasma, and actually found that the cells died more frequently.

Another study found that THC led to DNA damage and death in hippocampal neurons. They suggested that this may damage memory.

However, it should be noted that a few in vitro studies demonstrated neuroprotective effects of cannabinoids. Mainly, these protective effects were seen when neurons were overexcited, which can result in excitotoxic cell death. Cannabinoids were able to decrease neuron activity and impart protective effects.

Does cannabis kill brain cells in vivo?

Let’s first take a second to think about giving cannabinoids to live rats… That’s what these in vivo studies did.

This time, the question was whether cannabinoids could protect brain cells during traumatic events, like lack of oxygen.

The majority of in vivo studies found a neuroprotective effect for cannabinoids after brain injury. The authors attributed this to the neurons being less active (see ‘circuit breaker’). Astonishingly, the affected area of the brain in THC-treated rats could be reduced by 40%.

Interestingly, mammals appear to release their own cannabinoids in the brain after traumatic injury. The current working theory is that this happens to protect the brain.

In addition, some studies suggested that the protective effect of cannabinoids is due to its antioxidative capacity and ability to relax blood vessels.

THC and cannabinoids do not kill brain cells in in vivo studies. In fact, the opposite is true and cannabinoids have a neuroprotective effect after brain injury.

Conclusion

Overall, studies in live rats showed a protective effect of cannabinoids, such as THC, after brain injury. Initial clinical trials of the cannabinoid Dexanabinol, however, were unable to show benefits beyond the placebo effect. Yet, hopes for an effective cannabinoid treatment for traumatic brain injuries remain high.

Thus, the scientific evidence strongly suggests that cannabinoids, and therefore cannabis, do not directly kill brain cells – in fact in certain situations the opposite appears to be true. Of course, this does not mean that cannabis consumption is completely safe. There are long-term effects and especially effects on the brain development in adolescents, which are detrimental.

Great article: From synapse to society: https://www.nature.com/articles/npp2017255 – talking about the mechanism of eCBs, development and their use as pain relief.