The Dark Science of Marijuana

Added: 2026-05-04

[00:00:00]All drugs to some degree have negative side effects, especially when taken incorrectly or in excessive amounts.

[00:00:06]Most people probably know what drugs cause which effects. Alcohol can cause liver failure. Nicotine damages lungs.

[00:00:13]Cocaine can lead to heart attacks.

[00:00:15]Opiates have the potential to induce respiratory failure. And meth can result in brain damage and tooth decay. But what about marijuana? Can't really think of much, can you? Aside from sleepiness, some memory loss, and hunger cravings, there aren't really any harmful effects that come to mind. Sure, you could say smoking marijuana can cause lung cancer, but that goes for smoking tobacco, too.

[00:00:36]But also, you don't have to smoke it to get high from it. Compared to other drugs, marijuana is pretty tame. It's casually joked about that you can't overdose on it, even if you try. This has led people to believe that marijuana generally has no serious adverse side effects. Well, new research has found that it does, and it's nothing like you would expect. In the 1920s and 30s, there was a growing anti-marijuana movement after it was associated with Mexican immigrants who used it recreationally. Propaganda alleged marijuana caused insanity, made users prone to violence, and would cause moral decay of society. Anti-marijuana campaigns in the form of radio broadcasts, pamphlets, books, and films like Reef for Madness showed marijuana users as psychotic murderers and immoral deviants. Propaganda led to a social panic and marijuana was outlawed across the country in 1937.

[00:01:27]Now almost 90 years later, there may be a sliver of truth in this sensationalism. There is strong evidence that using marijuana can result in developing psychosis and/or schizophrenia. People are developing these mental disorders with no prior family history and symptoms are persisting when they are off the drug entirely. Marijuana produces a feeling of euphoria, relaxation, and mild pain relief. These effects are caused by the psychoactive compound tetrahydroinabonol or THC. The purpose of THC in the cannabis plant is to act as a defense mechanism to deter herbivores from eating it. THC causes disorientation, drowsiness, and in high enough doses, a reduced appetite. All of these effects would in some way or another discourage animals from eating it. What's also very interesting is the highest concentration of THC is stored in the flowering parts of the plant, which sit at the top. This would be the first part of the plant a grazing animal like a deer or cow would eat, thereby giving it the highest dose and strongest effects, in theory, sparing the rest of the plant. Humans discovered when THC is taken in smaller amounts, like being smoked or mixed with food, it can cause pleasurable effects.

[00:02:39]When THC binds to CB-1 receptors on neurons, it indirectly causes a release of dopamine in the body, producing the effects of euphoria. These CB-1 receptors are found on specific neurons called GABA neurons. It's called a GABA neuron because it releases a neurotransmitter called GABA. Imagine that. When no caninabonoids bind to CB-1 receptors, the neuron releases GABA neurotransmitters. GABA then binds to another neuron called a dopamineergic neuron, which as you may have guessed releases dopamine. When GABA binds, it essentially turns off the neuron, so it cannot release dopamine. Now, when canabonoids like THC bind to CB-1 receptors on GABA neurons, it prevents the release of GABA. With no GABA to turn off dopamineergic neurons, dopamine gets released. In effect, CB-1 receptors modulate how much dopamine gets released.

[00:03:31]It's not just external canabonoids like THC that bind to CB-1 receptors. Your body produces its own internal canabonoids called endockinabonoids to regulate dopamine. For example, your body releases an endockinabonoid called anatomide. Fun fact, anatomide is naturally found in chocolate. This is why you have a positive association and feel good when you eat chocolate. But anatomide only causes a very small release of dopamine. THC on the other hand binds much more tightly to CB-1 and causes a substantially larger release.

[00:04:04]However, because THC is so effective at causing a release of dopamine, it disrupts the balance of CB-1 receptors on neurons. The more CB-1 receptors are activated, the more dopamine gets released. If you can believe it, too much dopamine is actually dangerous. In large amounts, dopamine acts as a neurotoxin and damages neurons through oxidative stress. To prevent damage, the body decreases the number of CB-1 receptors in the brain so as to release less dopamine for protective measures.

[00:04:33]This is how and why you develop a tolerance to drugs. A small reduction in CB-1 receptors is natural. The body will slightly increase or decrease receptor count to make adjustments. However, a large reduction in receptors from excessive dopamine is not natural. This large decrease in CB-1 receptors is the root of the problem. Over time, the brain notices that dopamine levels have not spiked for a while. So, it increases CB-1 receptors. But sometimes too many receptors are added and too much dopamine gets released. The body goes back and reduces receptor count and later adds more when it tries to get back to normal. As a result, what you get is sporadic spikes and drops in dopamine which begin to distort the brain's ability to assess stimuli. This causes hallucinations and delusions due to a phenomenon called aberant salience.

[00:05:22]Salience is a heightened sense of priority the brain gives to an object or stimuli. Imagine you're walking in the woods and you hear the loud snap of a branch. You immediately alert to your surroundings and start scanning the area for source of the sound. The sound is salient because it stands out from the surroundings. Salience can be especially reinforced if an event causes a release of dopamine. For example, when an attractive man or woman smiles at you, your brain reacts with the small surge of dopamine. You replay the event in your mind, thinking of the person's face and how it made you feel. Salience paired with dopamine is an evolved mechanism that helps guide attention and facilitates learning by highlighting relevant or significant experiences. In aberant salance, the brain pays attention to random objects or events that are highlighted by unregulated and chaotic surges of dopamine. This causes the brain to hyperfocus on unimportant stimuli, creating hallucinations and delusions. To make matters worse, some CB-1 receptors are also located in the prefrontal cortex, which help control logic, cognition, and memory. Reduction in CB-1 receptors in the prefrontal cortex results in cognitive and memory deficits, making it more difficult to discredit the hallucinations. Despite evidence, however, there is hesitation by some groups that marijuana can cause psychosis. Skeptics point to evidence of widespread marijuana use in the 1960s and 70s. If THC really has the potential to cause psychosis, there would have been a noticeable increase in psychotic cases across the country. While this is a good argument, it doesn't have all the facts. THC in marijuana today has a much higher potency than it did decades ago.

[00:07:00]In the 1960s and 70s, the average potency of THC in marijuana was 2%.

[00:07:06]Today, due to advances in agriculture techniques and genetic crop farming, the average THC potency is between 17 and 28%. Roughly 10 times higher. Decades ago, there wasn't a legalized marijuana economy that sold a variety of cannabis products. In addition to the marijuana flour, you can easily buy THC oils and tinctures with potency as high as 95% and marijuana edibles. In Colorado, THC concentrate and edible products accounted for 48% of all marijuana sales in 2025. Why is this relevant? People are using high concentrated THC and edibles more than ever before. The high volume of marijuana edibles is especially concerning because when ingested, the THC is metabolized in the liver and converted into 11 hydroxy THC.

[00:07:55]11 hydroxy THC is two to three times more potent than THC and lasts twice as long in the body. This is why you cannot draw a parallel to marijuana use in the 1960s and today. However, THC potency is not the only reason. For decades, marijuana was not widely available for research in the US. It was labeled as a schedule one drug in the 1970 Controlled Substances Act, making it nearly impossible for scientists to obtain for research. Had marijuana been more accessible for research, scientists may have made discoveries on its potential to cause psychosis much earlier. While marijuana was restricted for research in the US, countries in Europe were starting to collect their own data on THC. One of the first studies that discovered the link between marijuana and psychosis was a Swedish conscript study published in the Lancet in the 1990s. Researchers tracked 50,000 men in 1969 and 1970 who were conscripted to join the Swedish military at the age of 18. Their lifestyle and drug habits, if any, were documented over a 15-year period. Data was collected through hospital and medical records. Scientists determined that Swedish conscripts who use cannabis by the age of 18 had a 2.4 times higher risk of developing schizophrenia. A 27-year follow-up was later conducted on participants that found a dose and frequency relationship between marijuana use and schizophrenia.

[00:09:19]While the Swedish study showed long-term effects from marijuana over several decades, another study from Canada showed something even more interesting.

[00:09:27]Effects of marijuana on a population before and after legalization. A Canadian study published in JAMAMA tracked medical records of 13 million subjects between 2006 and 2022 who had no history of schizophrenia. Medical records were observed before and after marijuana was legalized. Before legalization, the rate of schizophrenia cases in Canada was 3.7%. After legalization in 2012, schizophrenia rates increased to 10.3%.

[00:09:55]A three-fold change, while psychosis cases doubled. The largest group affected were men between the ages of 19 and 24 and accounted for 19% of new cases. A similar outcome was found in Colorado after legalization. Prior to cannabis being legal between 2005 and 2012, psychosis cases in Colorado averaged around 22 per 100,000. After legalization, data collected between 2012 and 2020 found psychosis cases had increased to 32 per 100,000, a 47% increase. The two most common factors in these studies that predicted developing psychosis or schizophrenia were age and frequency of use. The younger the age, the higher the risk of developing a mental disorder. This was a consistent finding in the Swedish study. Recruits who started taking marijuana at or before the age of 18 had higher outcomes of psychotic and schizophrenic behavior later in life. It's theorized that early marijuana use can halt important brain development, causing alternative neural pathways to form that reflect psychosis.

[00:10:59]As a result, the individual continues to behave and grow within a mentally altered brain. In addition to age, frequency of use matters, too. Using marijuana several times a week, especially with higher potency THC, raises your tolerance and reduces CB-1 receptors. This in turn creates an environment that makes it conducive for aberant signaling, which mimics mental illness. Lastly, genetics plays a big role in how people respond to THC.

[00:11:26]People with certain genetic variations can develop psychotic symptoms faster and more easily than others. For example, the COOMT gene codes for an enzyme that clears dopamine. People with a variant of the COOMT gene code for an enzyme with higher dopamine clearing activity. This puts them at a higher risk of developing psychosis from repeated marijuana use. In summary, under the right conditions and behavior, marijuana can cause psychosis or schizophrenia. Using at a young age, high in frequency, and genetic predispositions all increase the chances of developing a mental disorder. It's also worth noting THC has a potency 10 times higher than it did 50 years ago.

[00:12:04]At the end of the day, THC is a drug and a psychoactive one at that. It should be viewed as a medicinal substance that can be used for treatment and if possible under the direction from a medical professional. All drugs, no matter how harmless they may seem, have side effects. And now you know what effects marijuana has. Thank you for watching Dark Science.