Due to the US-led global war on drugs, propaganda campaigns have introduced vast amounts of misinformation regarding the use of cannabis and other drugs. This has caused a large amount of confusion regarding both the effects of cannabis, and the potential dangers associated with it. Because of this, some people think that smoking cannabis can cause hallucinations, a property of drugs such as LSD, psilocybin, dimethyltryptamine, among others. Although certain users may also claim that they have had these experiences, in this article we are going to move away from anecdotal claims and look into what the science says regarding whether or not too much weed can cause hallucinations.

Hallucinations from Cannabis

Having true hallucinations from whole plant cannabis ingestion is extremely rare in the literature. In a 1986 review, it was found that patients with pre-existing mental health conditions, such as schizophrenia, bipolar disorder, or depression, could experience psychosis with cannabis consumption. The authors also found one study in which heavy cannabis users in Jamaica reported auditory hallucinations, but little information on the previous mental state or history of the subjects was given. The same review also looked at many other studies, such as one involving 720 military personnel who used hashish, and noted that it was “tolerated quite well” with very few examples of psychosis, except when mixed with alcohol or other drugs.  A 2018 clinical trial attempted to quantify hallucinogenic experiences by providing participants with previously diagnosed psychiatric conditions,  different hallucinogenic drugs such as psilocybin, dextromethorphan (DXM), and extract of Salvia divinorum. Each of these cause hallucinations through different mechanistic pathways, and were compared with cannabis smoking or oral consumption. Although some subjects reported strong psychoactive effects, the authors of the study did not believe that these were truly ‘hallucinations’ as compared to the other drugs trialed. Furthermore, they concluded that neither THC nor the other cannabinoids or terpenes present in the cannabis plant activated the same receptors (5HT-2A, k-opioid, or NMDA) in the brain as the other hallucinogenic drugs. Indeed, according to most of the literature available, hallucinations from whole plant cannabis (with its constituent cannabinoids and terpenes) is extremely rare in healthy individuals with no family history of psychiatric illness.

Hallucinations with Pure THC

Studies that have used synthetic THC rather than whole plant cannabis have obtained vastly different results, with much more heterogeneity between user experiences. Across the literature there are accounts of psychotic episodes involving the consumption of pure THC, which has become more popular as pharmaceutical companies attempt to circumvent the medical marijuana industry and clandestine chemists flood the black market with drugs like “K2” and “Spice.” In a 2005 study using the synthetic THC Dronabinol, two patients out of 22 experienced uncomfortable and severe psychotic episodes, including delusion, depression, anxiety, and the inability to perform psychometric tests. Both were previous cannabis users, who had never reported such strong negative side effects. However, it is difficult to draw any concrete conclusions from this study, due to the small sample size. In addition, complications such as an underlying psychiatric condition could be a factor in inducing psychosis from synthetic THC. More research needs to be conducted using randomized, double-blind, placebo-controlled trials before any further conclusions can be drawn. In the 2018 study, funded in part by the National Institute on Drug Abuse (NIDA), it was concluded based on a review of several studies that “the peer-reviewed reports that do detail hallucinogenic experiences in healthy adults predominantly come from research studies involving the administration of purified THC.” They go on to discuss the problem of such studies, and the consequences they have on the perceptions of cannabis and human health and related policy decisions. 

Hallucinations in Those Predisposed to Psychosis 

Some media reports indicate that cannabis consumption can led to psychotic episodes or schizophrenia, which is largely described by both auditory and visual hallucinations. However, most studies show that this is only a factor in patients with a predisposition or family history of psychological issues. It was presumed that cannabis could ‘awaken’ latent psychiatric disorders, a claim also made against drugs like LSD. Even as far back as 1976, scientists were comparing the effects of what they termed ‘cannabis psychosis’ with schizophrenia, but some of the studies had problems with research methodology and the subsequent interpretations of the findings. Recent studies have largely refuted this hypothesis, although there is some correlation, there is very little evidence for a causative relationship. A 2007 article in the Journal Schizophrenia Research looked at nearly 760 cases of first onset schizophrenia and compared those who had used cannabis and those who have not. They concluded that there was “no statistically significant effect of cannabis use” in the expression of psychotic episodes. They did however find that those using cannabis had less “accusatory hallucinations’ than non-users. After comparing the data to family history, the study concluded that there was no evidence for a link between cannabis consumption and schizophrenia. This study is very interesting because it goes against other studies cited thus far by suggesting that cannabis use does not induce psychosis in schizophrenia patients anymore than in the general population. This outlier shows how much more research there is to do on cannabis’ relationship with schizophrenia before the scientific community can draw a consensus. A 2010 study in the British Journal of Psychiatry found that, in general, psychiatric patients who also used cannabis did less well than those who did not. However, when it came to schizophrenia and hallucinations they concluded that there was ample evidence to show that cannabis reduced negative symptoms, even though more hallucinations were reported amongst the cannabis using group than the control group. The study warns that current understandings of these relationships is lacking, and that those with known psychotic disorders should avoid using cannabis.  

So, Will I Hallucinate on THC?

As shown in the literature and discussed above, the chances of any healthy person hallucinating when smoking or consuming cannabis is extremely low. Also, such experiences described by users have been shown to be mechanistically and experientially not the same as true hallucinogenic drugs like LSD, DMT, Ketamine, DXM, or salvia divinorum. However, caution should be taken regarding the consumption of pure or synthetic THC, which, without its’ entourage compounds, can elicit uncomfortable, acute, psychotic states. Care should also be taken by those individuals suffering from a diagnosed mental disorder, or with a family history of psychiatric disorders. 

The Effects of THC

The cannabinoid THC is a known psychoactive compound which activates parts of the endocannabinoid system in the body, primarily the CB-1 receptors in the brain. Depending on the individual and the strain of cannabis ingested, effects can range from euphoria, bliss, and relaxation to anxiety, paranoia, and depression. For the most part, users report enjoyable experiences, and except in the case of over-consumption, negative experiences are rare. However, this statement applies mostly to the consumption of THC in cannabis, and changes when we talk about the consumption of pure or synthetic THC.  In more recent years synthetic THC has been used in research, and unfortunately has become a prominent street drug in place where cannabis is illegal, such as the UK. Researchers are starting to understand the pronounced negative effects of synthetic THC that users have self-reported.  This information is presented for informational purposes only, and is not intended to diagnose, treat, cure or prevent any medical condition.  Please always consult your own doctor.