Experts are warning that potent marijuana may lead to serious mental health issues, including schizophrenia and psychosis. 

In the United States, cannabis usage has almost doubled over the last decade, with 21.8 percent of individuals aged 12 and older—amounting to 61.8 million people—reporting using cannabis in 2023, a significant rise from 12.6 percent in 2013.

The THC content, which is the psychoactive compound causing the ‘high’ associated with marijuana consumption, has seen an increase in most strains. Currently, THC levels are typically between 20 to 30 percent.

This is a significant rise from 1995, when the average batch of marijuana seized by the DEA had a THC content of four percent. 

But in some weed pens and vapes, THC can reach percentages in the 90s. 

In a new study, researchers from Massachusetts and Colorado explored the effects of marijuana products with high concentrations, specifically those with at least 5mg of THC or more than 10 percent of the compound per serving.

They reviewed data from 99 studies that included 221,097 cannabis users. 

Almost two-thirds (61 percent) of the studies included participants between the ages of 18 to 59, with 4 percent involving adolescents. Their analysis revealed that 70 percent of the studies identified a negative association between cannabis products containing over 10 percent of THC per serving and the development of psychosis or schizophrenia.

Experts highlight the risk of psychosis associated with cannabis products high in THC content, based on a new comprehensive study (stock image).

Cannabis is becoming more accessible and potent, with the graph indicating attributes of smokable cannabis. Other formats, such as vape products, can contain up to 98 percent THC, the psychoactive component in the drug linked to psychosis.

The association with psychosis or schizophrenia was identified quickly, even during the first 12 hours of use and was present at follow-up of up to two months. 

They did not mention how the frequency of cannabis use impacted the onset of mental health issues. 

Author of the study Dr Jonathan Samet, professor of epidemiology and environmental and occupational health at the Colorado School of Public Health, said: ‘The findings are concerning and warrant a precautionary approach to using cannabis products, particularly for those with preexisting psychosis.’ 

One of the most recent shocking cases of cannabis-induced psychosis which made headlines involved Bryn Spejcher of Thousand Oaks, California, who picked up a bread knife and stabbed her new boyfriend 108 times – killing him – before turning the blade on her dog.

The then 32-year-old, who worked as an audiologist, then proceeded to stab herself – only stopping when police hit her nine times with a baton.

In December 2023, Spejcher was convicted of killing her boyfriend – Chad O’Melia, then 26.

However, testimony from an expert witness called by the prosecution, seen exclusively by DailyMail.com, paints a vastly different picture of the perpetrator than the story would initially suggest. 

Forensic psychiatrist and expert witness Dr Kris Mohandie told the jury that Spejcher was a ‘normal’ girl with ‘no history of mental illness or violence’ who was committed to ‘doing good’ in the world.

That fateful night her brain was completely overtaken by extreme psychosis – induced by potent marijuana that had been supplied by her boyfriend, he said. 

In testimony from Spejcher herself, the healthcare professional said she’d smoked weed only a few times before, and had ‘never been high’.

Her attack was launched because she had ‘lost touch with reality’, as the cannabis had triggered ‘voices in her head’.

Following a growing number of cases echoing Spejcher’s, more studies have focused on the harmful impacts of potent cannabis, especially when it comes to mental health issues. 

The studies assessed in the recent investigation looked at people using cannabis both for recreational purposes and therapeutically. 

Medicinal marijuana is commonly used to treat various conditions such as chronic pain, chemotherapy-induced nausea, and epilepsy.

The researchers also look at how cannabis impacted depression and anxiety, with mixed results. 

32 year-old Bryn Spejcher was said to be suffering a severe case of cannabis-induced psychosis when she brutally murdered her boyfriend in May 2018

In nontherapeutic studies, participants reported worsening anxiety in 53 percent of the cases and depression in 41 percent of the investigations. Healthy participants – those with no underlying conditions – were the most prone to these effects.

In therapeutic studies, looking at how cannabis helps treat medical conditions, patients experienced relief from anxiety and depression in half of the cases. Those with cancer and neurologic conditions experienced the most benefits for anxiety.

The study also found 75 percent of the studies were associated with users developing an addiction to the drug known as cannabis use disorder. 

This is a mental health condition where a person compulsively uses cannabis despite experiencing significant impairment or distress in their daily life, leading to negative social, occupational, or health consequences.

As cannabis use has increased, the population prevalence of cannabis use disorder has risen in the US. 

In 2023, almost one third of those who reported using cannabis, met criteria for cannabis use disorder.

Several factors have contributed to this surge, experts say, including the decriminalization and legalization of recreational cannabis, and the increasing availability of cannabis products in legal markets.

While marijuana is still illegal at the federal level, it is fully legal in 24 states, plus Washington DC. 

More than half of Americans live in states where recreational marijuana is legal, and 79 percent live in a county with at least one dispensary, according to the Pew Research Center. 

The recent study comes of the back of another body of research that was published in the Canadian Medical Association Journal last month.

It revealed that patients needing hospitalization because of cannabis-related health problems were 14 times more likely to develop schizophrenia within three years.

Modes of marijuana use in 2023 among people aged 12 or older in the US

These symptoms could range from severe psychiatric symptoms such as paranoia or panic attacks to overdosing on THC.

Researchers found that the risk for schizophrenia was 241 times higher among people needing hospitalization for cannabis-induced psychosis.

This temporary mental health condition triggered by cannabis use causes hallucinations, delusions, and disorganized thinking.

The report found that the main cause of this major health risk was the significant rise in the levels of THC within cannabis.

Dr Nicholas Fabiano from the University of Ottawa said: ‘Cannabis from the 2000s is not the same as in 2025.’

While schizophrenia itself is not a fatal condition, it can lead to life-threatening situations as these patients have a higher risk of dying by suicide due to severe symptoms such as depression.

Overall, the report revealed that about 0.47 percent of cannabis users end up experiencing symptoms of psychosis. That’s roughly one in every 200 users.

However, up to 76 percent of those who do experience these symptoms for more than 24 hours end up needing emergency care – sending their chances of developing schizophrenia skyrocketing.

Schizophrenia is treated with a combination of antipsychotic medications, therapy, and support.

Antipsychotic drugs, like risperidone and olanzapine can help manage symptoms such as hallucinations and delusions by balancing brain chemicals. 

Therapy, such as cognitive behavioral therapy (CBT), can help patients cope with symptoms and improve their daily functioning.