Reefer Madness, the classic American anti-cannabis propaganda film, was released in 1936. It painted cannabis as an extremely dangerous drug that causes madness, irrational and dangerous behavior, and an uncontrollable desire to commit violence. This “information” came largely from rumors and from the racist anti-immigrant lies spread by Harry J. Anslinger, the then-commissioner of the US Treasury Department’s Federal Bureau of Narcotics.
These days, most people see cannabis as a relaxing, mostly harmless drug. According to statistics, it should be safer than alcohol for most users, and its negative side effects are rarely significant. However, “reefer madness” isn’t gone completely. In Tell Your Children: The Truth About Marijuana, Mental Illness, and Violence, Alex Berenson claims that “the black tide of psychosis and the red tide of violence are rising together on a green wave, slow and steady and certain. All anyone needs to do is look.”
This passage from the book struck me as more than a little bit melodramatic, and absolutely reminiscent of Reefer Madness. No surprise there – “Tell Your Children” was the original title of Reefer Madness while the movie was still in production. But, despite the author’s obvious bias and, ah… “creative” interpretation of several scientific studies, I couldn’t dismiss the book’s topic completely.
There are studies that show a relationship – a strong correlation, if nothing else – between cannabis and schizophrenia. Anti-cannabis advocates like Berenson claim that it has been “proven” that cannabis causes schizophrenia. On the other hand, cannabis advocates may downplay the connection, obscuring the truth in the same way that Big Tobacco did when scientists became convinced that cigarettes caused cancer, but hadn’t definitively proved it yet. This deception may or may not be happening, but it’s a valid concern.
In any case, anyone who claims to know “the truth” about the relationship between cannabis and schizophrenia is lying. There have been studies, but not enough. The studies that have been done are rife with limitations. Books been written, but they’re heavily biased and untrustworthy. Data has been analyzed, but confounding variables introduce uncertainty. Conclusions have been drawn, but they’re premature in relation to scientific fact and often based on paranoia or wishful thinking.
This essay will cover everything that we know for a fact about cannabis’ relationship to both psychosis and schizophrenia.
Psychosis Vs. Schizophrenia
Before we really get into this topic, we need to clarify the difference between psychosis and schizophrenia. Psychosis is a symptom, not an illness, and usually involves hallucinations, delusions, or both. People suffering from psychosis may hear voices, see objects or people that are not really there, and experience strange, unsettling sensations. They may also suffer delusions of varying severity, such as believing that their friends mean them harm, that they are being controlled by outside forces, that they’re somebody else, or that they have some sort of special power. They may also present with disorganized speech or strange physical behavior.
Schizophrenia is a mental disorder that is accompanied by psychosis. Unlike psychosis itself, which can have several causes and can be temporary, schizophrenia is chronic and currently has no cure. People suffering from schizophrenia may experience episodes of severe delusions, hallucinations, and disorganized thinking that can last for months. These are the disorder’s “positive” symptoms. Schizophrenia may also have “negative” symptoms like a decline in personal hygiene, a lack of emotion, and anhedonia – an inability to feel pleasure. Schizophrenia is a very severe disorder, and in many cases, can be disabling.
Cannabis And Psychosis
Regardless of cannabis’ potential relationship to permanent mental disorders like schizophrenia, we know for a fact that cannabis can cause psychosis. In high enough doses, cannabis can cause psychosis that lasts several hours, even in healthy individuals who do not have a psychotic disorder. These episodes are transient and are not likely to increase the likelihood of future schizophrenia. On rare occasions, episodes can last 48 hours or more, in which case they will be officially diagnosed as cannabis-induced psychosis (CIP). Regardless of the duration, these episodes may consist of paranoia, delusions, a loss of touch with reality, and hallucinations. Fortunately, unlike a psychotic episode stemming from schizophrenia, a CIP episode usually resolves within a week.
Individuals who have a family history of schizophrenia are more likely than others to experience an episode of cannabis-induced psychosis, if they choose to use cannabis. At this point, the implications of this fact are unclear. Up to 50% of CIP cases eventually convert into permanent schizophrenia, and people who have experienced CIP seem to be more likely to develop schizophrenia.
This could mean that cannabis can cause psychosis, even in healthy individuals, and that psychosis raises their chances of developing schizophrenia. However, some of these episodes of CIP may actually be the first episode of schizophrenia, which was latent until cannabis triggered it but existed prior to any cannabis use. Many times, short-lived (one month or less) cases of CIP do not lead to schizophrenia or any other psychotic disorder, but may still increase the sufferer’s chances of having another CIP episode in the future.
Clearly, any individual’s chances of experiencing a psychotic episode – drug-induced or otherwise – are dependent on a handful of factors. At this point, what we know for sure is that cannabis use can cause temporary psychosis. This is more likely to happen to individuals with a family history of psychotic disorders, and the chances of this occurring increase along with the amount of cannabis used and the regularity of that use.
What Should I Do If I Experience Psychosis?
First of all, don’t panic. If your episode of psychosis lasts long enough to be diagnosed as CIP, you still probably won’t develop schizophrenia. If your psychotic episode lasts less than 48 hours, it shouldn’t increase your risk of future schizophrenia. However, whether you experience transient psychosis or a 48+ hour of CIP, you should seek medical help. If your episode is short-lived, counseling can help you move past the experience more quickly. And, if you do unfortunately develop a psychotic disorder, early treatment has been shown to result in a better-managed illness and much better long-term outcomes.
Psychosis vs. “Positive Psychotic Symptoms”
When reading studies, articles, and other literature about cannabis and psychosis, it’s important to make a distinction between psychosis and “positive psychotic symptoms.” One study gave 22 healthy adult males a dose of 2.5 mg of THC (a fairly small dose) and found that the THC induced transient psychotic symptoms. That sounds alarming, but what are the researchers counting as psychotic symptoms?
According to one source, positive psychotic symptoms are defined as: auditory, visual, tactile, or gustatory (relating to smell) hallucinations, delusions, paranoia, and disorganized thoughts or speech. Clearly, some of these are on a different level than others. If cannabis causes a user to hallucinate threatening voices, that may be indicative of an underlying problem. However, if the user experiences mild alterations to his or her senses and has disorganized thoughts and speech due to a reduction in short-term memory, it’s unlikely that anything negative is happening – those things are just normal parts of the cannabis high. The fact that many studies don’t clarify which symptoms their subjects experience is a shortcoming, and can lead to a significant exaggeration of cannabis’ risks if psychosis and minor psychotic-like symptoms are conflated.
Cannabis And Schizophrenia: The Case For A Causal Relationship
In Alex Berenson’s book Tell Your Children, the author relies heavily on two studies that seem to support his position the most strongly. The results are alarming, with one study showing that compared to those who had never used cannabis, “heavy users” – cannabis users who used more than 50 times by age 18 – were 6 times more likely to be hospitalized for schizophrenia by the age of 33. At face value, that’s very alarming. Fortunately, that figure might be a little bit dramatic, as it doesn’t account for all of the variables.
For instance, schizophrenia is linked much more strongly to cannabis use during childhood and adolescence than it is to adult use. Simply waiting until age 21 or 25 to start using cannabis drastically reduces any effect cannabis may have on the development of psychosis or schizophrenia. Further, that “six times” figure didn’t take into account some of the confounding variables. When psychiatric factors, family backgrounds, social backgrounds, and the use of alcohol, tobacco, and inhalants were controlled for, the correlation between cannabis and schizophrenia became much smaller.
Unfortunately, the study does not control for these variables in the group designated as “heavy users,” so a direct comparison can’t be drawn. What the study does tell us is that in the group of users who had used cannabis between 10 and 50 times, the risk of developing schizophrenia went from 3x to 2x when other variables were controlled for, and was deemed statistically insignificant. This omission of a controlled-for “heavy users” group is only one of this study’s limitations, so more research is obviously in order.
Other research has yielded conflicting results. A handful of studies have suggested a strong correlation between cannabis and schizophrenia, and the connection seems to grow stronger when users consume cannabis in either higher-potency forms or with more frequency. On the other hand, there are also a handful of studies that found that the relationship between cannabis and schizophrenia is likely not causative.
For example, one study conducted by Harvard Medical School in 2013 found little evidence to support cannabis use as a cause of schizophrenia. Researchers gathered data about 282 subjects’ histories of cannabis use and family histories of psychotic disorders (or lack thereof), and found that having an increased familial risk for developing schizophrenia was the underlying cause in their sample, not cannabis use.
Cannabis And Schizophrenia: The Case Against A Causal Relationship
Studies have shown that there is a definite correlation between cannabis use and schizophrenia, but the nature of that relationship is unproven. There are a few pieces of evidence that contradicts the idea that the relationship is causative, though.
For one, it is believed that cannabis has become much stronger since the 1960s, containing 10% or more THC versus around 2%. This may not be accurate. The cannabis that gave us the 2% figure was seized in home investigations, and may have degraded over time, showing a lower amount of THC than it would have had when it was fresh. However, if we assume that cannabis really has gotten 40 times stronger than it was in the 60s, we should see the rate of schizophrenia diagnoses rise alongside rising amounts of THC. This has not happened, which may mean that the relationship isn’t as causal as some people think. Even if cannabis potency has stayed the same over the years, the prevalence of cannabis use is rising – but schizophrenia rates have remained the same, and have even dropped in some countries.
An individual’s likelihood of getting schizophrenia is influenced by a multitude of factors: family history, socioeconomic situations, family situations, the age of an individual’s father, malnutrition, and more. It’s complicated, but most neuroscientists believe that schizophrenia is essentially a neurodevelopmental disorder, and that whether or not someone will develop the condition is decided almost entirely during gestation of the fetus.
The evidence supporting this belief comes from brain scans and autopsies of schizophrenia sufferers, which show that certain parts of a schizophrenic brain are malformed. If this malformation were to happen during adulthood – from smoking cannabis, say – scientists would be able to observe large amounts of glial cells gathering in the “holes” left by destroyed neurons. This process does not occur in schizophrenic brains, which is a clue that the malformed regions of the brain likely developed that way during gestation or during early childhood.
If this is the case, it would mean that cannabis cannot cause schizophrenia – it just hastens the onset of the disorder in individuals who likely would have developed it anyway. That’s something to avoid, obviously, but it’s good news for healthy cannabis users. Additionally, if schizophrenia is a neurodevelopmental disorder, that would help to explain why findings have shown that use during adolescence is so much more likely to contribute to the development of schizophrenia – until age 25 or so, the brain is still developing and vulnerable, and could still be damaged by heavy cannabis use.
Does Schizophrenia Lead To Cannabis Use?
Some researchers have argued that rather than cannabis use causing schizophrenia, schizophrenia causes sufferers to use cannabis to self-medicate. Others argue that perhaps the genes that predispose individuals to schizophrenia also predispose them to cannabis use. In a response to the Lancet study that claimed that the incidence of psychosis would drop significantly if high-potency cannabis were not available, a group of scientists stated: “We… found a consistent pattern of evidence supporting a causal effect of schizophrenia risk on lifetime cannabis use. By contrast, we found little evidence for any causal effect of cannabis use on schizophrenia risk.” It should also be noted that in terms of overall rates of drug-induced psychosis, alcohol causes more instances of psychosis than cannabis.
The idea that schizophrenia sufferers use cannabis to self-medicate is plausible, even if intuitively that doesn’t make sense – after all, if we know for a fact that cannabis use can worsen schizophrenia symptoms and even trigger psychotic episodes, why would anyone try to treat the disorder with cannabis? The obvious answer is that while THC has been shown to worsen psychotic symptoms, CBD improves them, but there are other explanations.
One interesting study found that people who had schizophrenia and used cannabis often had better cognitive function than non-users. However, this study has some significant limitations: the sample size of 99 is very small, and the highest frequency of cannabis recorded was “daily,” which doesn’t give us any idea about what kind of difference smoking a joint vs. a half-ounce per day makes. The study’s findings were that while cannabis use seemed to result in better cognitive function, less dysphoria, and more sociability early in the disorder’s progression, cannabis users also exhibited symptoms earlier, experienced their first psychotic episode at a younger age, spent more time in the hospital, and experienced more disorganization as well as more positive and negative symptoms. Clearly on balance, cannabis use for people with schizophrenia or predisposition to schizophrenia is still a terrible idea, but the short-term benefits may explain why people with schizophrenia or pre-psychosis symptoms might use cannabis to self-medicate.
What Are The Odds?
Schizophrenia is a severe, often disabling condition. The stories of individuals who suffer from the disorder can be terrifying, which makes the idea that cannabis could cause schizophrenia – whether or not that proves to be the case – equally frightening. But if you look at the numbers, you’ll see that it probably isn’t time to panic just yet.
Rates of schizophrenia diagnoses vary from country to country, but the worldwide average is approximately 0.7%, meaning that less than 1 in every 100 adults will be diagnosed. For individuals with a family history of schizophrenia, the numbers are higher – 13% for the child of a schizophrenia sufferer, ~18% for a sibling, and potentially up to almost 50% for an identical twin (though that number may be lower). For this reason, anyone with a family history of schizophrenia should avoid cannabis entirely.
So, assuming you’re healthy, don’t use cannabis or any other drugs, and have no family history of schizophrenia, you have a 0.7% chance of being diagnosed with the disorder. If you want to adjust for the possible increased risk posed by cannabis use, the number you multiply that 0.7% by depends on which study you look at, and it isn’t straightforward – many of the studies, being short-term, only looked at the prevalence of first-episode psychosis, not full-blown schizophrenia. At worst, the Lancet study found that daily use of high-strength cannabis could increase the risk of a psychotic episode by a factor of 4.8. Multiplied by 0.7%, you get 3.36%. In other words, your risk of developing psychosis in these conditions is less than 1 in 20.
That’s not so bad, especially when you remember that those are the odds of experiencing psychosis, not schizophrenia. Out of all the cases of cannabis-induced first-episode psychosis, less than half (47.4%) convert to either schizophrenia or bipolar disorder. So, perhaps it would be most accurate to say that if you use high-potency cannabis every day, you may have a 1.59% chance of developing schizophrenia – slightly more than double a healthy non-user’s odds. That number may increase for users who start in their teens, and it will decrease for anyone who smokes less potent cannabis or who smokes less than every day. If you want to continue enjoying cannabis while minimizing your chances of experiencing psychosis and possible (though unlikely) schizophrenia, what should you do?
Staying Safe While Stoned
First of all, I’ll reiterate that we don’t know that cannabis can cause schizophrenia. There are indications that there could be a causal link between the two, but it hasn’t been proven, and the correlation does have other explanations. However, it is likely that cannabis use does slightly increase the user’s risk of psychosis.
If you have a family member with schizophrenia or other psychotic illnesses, you should avoid cannabis completely. If your family history is clean, the most important thing you can do to avoid any potential harm is to abstain from cannabis until adulthood, preferably until the age of 25. During the early 20s, the brain is still developing and is somewhat vulnerable, though not nearly as much as it is during the teenage years.
Next, pay attention to your experiences and perceptions when you’re high. If you have strange hallucinations or strong psychotic-like symptoms, they may be indicators that you have some predisposition to psychosis. As a general rule, if cannabis makes you uncomfortable, you should probably quit using it.
Pay attention to your dose, and don’t overdo it. Most episodes of CIP happen when a user smokes too much, or (more commonly) takes too many edibles. Cannabis appears to be mostly harmless, but it does need to be used with some care.
Finally, control your levels of cannabis use. Higher rates of use are associated with a higher risk of psychosis. You can easily lower your odds by smoking smaller amounts of cannabis less frequently.
If cannabis does cause damage to structures in the brain, that’s likely because THC is slightly neurotoxic. That means that any brain damage is a result of the amount of THC that goes into your body, and not a result of how high you get. This is another reason to keep your THC tolerance down – if you want to get blasted, you’ll be much healthier if you maintain your ability to do that with two hits instead of twenty.
The gaps in the research regarding cannabis’ relationship to schizophrenia are frustratingly large, and there’s a lot that we don’t know. The research that has been conducted is rife with limitations, and interpretations of the data vary. If cannabis really causes schizophrenia, as some researchers believe, we may see a rise in schizophrenia diagnoses. However, if that was the case, we should have seen that rise already.
As research continues, we’ll get a better idea of how all of this really works. In the meantime, don’t worry unduly – even if the relationship between cannabis and schizophrenia is causative, even the heaviest use still poses a relatively small threat to an individual user. If you practice moderation and avoid teenage cannabis use, statistics are on your side.