The potency of marijuana has been rising for the past 50 years, with THC levels in some cannabis products now close to 100 percent. Consequently, there is a serious concern for the impact on health – particularly for young people, whose brains are still developing.
Increase in Potency
The main psychoactive ingredient in marijuana is tetrahydrocannabinol (THC), which stimulates the area of the brain that responds to pleasure. This causes dopamine – the chemical responsible for feelings of joy, satisfaction, and relaxation – to be released.
The other ingredient in marijuana is cannabidiol (CBD), which when administered alone is not intoxicating or associated with a risk of dependency at typical doses. CBD is increasingly recognized for its potential medicinal uses,  including the treatment of psychosis and addiction. When marijuana contains a certain combination of THC and CBD, research shows that CBD may moderate the effects of THC and potentially reduce or mitigate the acute effects of THC on psychotic-like symptoms.
Concentrations of THC and CBD vary considerably across different cannabis products, which greatly impacts the health risks for the user. Recent research has found that, between 1970 and 2017, the quantity of THC in a typical gram of cannabis rose by 2.9 milligrams each year for all herbal cannabis and by 5.7 milligrams each year for cannabis resin. There are now concentrated THC products available, such as oil and edibles that have a THC concentration upwards of 95%.
The Dangers of Stronger Cannabis
A new study, published in The Lancet Psychiatry, advises that individuals consuming high-potency marijuana are more likely to experience addiction than those using low-potency products. Findings also suggest that those using high-potency cannabis are more likely to experience a psychotic disorder, such as schizophrenia.
Many are unaware of the significant increases in potency in the last 50 years or the sharp increase in the past 10 years with the release of new THC-concentrated products. There are concerns that the medicinal properties of marijuana are not present in these high-potency products and do more harm than good. There are particular concerns for young people, who have access to cannabis products but little understanding of their potency or risk. The rise in vaping among young people has further increased the accessibility of cannabis products that are almost undetectable to parents or educators yet come with potential dangers.
There are particular risks of heavy, high-potency marijuana use starting in adolescence, as it is a time of significant brain development. Longer-term effects of cannabis are of particular concern in those under 18 who abuse the drug. Smoking marijuana before age 18 may affect how the brain builds connections for functions such as attention, memory, and learning. This could last a long time or even be permanent. Drug use, including marijuana abuse as a teenager, increases the chance of developing a cannabis use disorder.
Risk Factors for Psychosis
Several studies have shown that high-potency marijuana use increases the risk of developing a psychiatric disorder, such as psychosis, Recent research suggests that smoking high-potency marijuana every day could increase the risk of psychosis by almost five times compared to people who have never used marijuana. The quantity of the drug used, in addition to the age at first use and genetic vulnerability, are all shown to affect this relationship.
Recent research has found that an increased risk of developing psychosis is directly linked to a specific genetic vulnerability. People who consume cannabis and also carry a specific variant of the AKT1 gene are at an increased risk of developing psychosis. The AKT1 gene codes for an enzyme affecting dopamine messaging in the striatum, which is the input module to the basal ganglia. One study found that the risk of psychosis among those with this variant was seven times higher for those who used marijuana daily compared with those who used it infrequently or used none at all
Cannabis and Substance Use Disorder
The debate about marijuana and addiction is long-standing. Many remain convinced that marijuana is not an addictive substance and that marijuana dependence does not occur. Research, however, argues differently. THC can cause dependence, both physical and psychological.
Around 4 million people in the US meet the criteria for marijuana dependence , with rates much higher in young people. The chances of becoming addicted to cannabis after consuming it across a lifetime is 8.9%, which, while significantly lower than other drugs like cocaine, still presents a significant risk to marijuana users.
Those who start smoking marijuana before age eighteen are up to seven times more likely to develop a marijuana use disorder. The full extent to which consuming marijuana in adolescence affects brain development is still unknown, however.
It is understood that heavy cannabis use over time causes the brain to produce fewer endocannabinoid neurotransmitters. These are naturally produced by the brain, but consistent cannabis consumption causes the brain to adapt to higher levels of THC, which resembles cannabinoids. When the brain has adapted by producing fewer endocannabinoid neurotransmitters, stopping cannabis consumption can cause withdrawal symptoms and make it difficult to quit.
Importance of Awareness
With cannabis products now legal in several US states, many adults consider it safe. While millions of Americans consume marijuana in moderation each month without danger to health, there is increasing evidence of the harm caused by heavy or high-potency cannabis use. Currently, Vermont and Connecticut are the only states in the US that cap THC potency on most forms of cannabis products. Increasing awareness of the dangers of high-potency cannabis is an essential step for mitigating risk and ensuring that adults know the changes in potency that have occurred in the past 40 years.
In addition, there are calls for other measures to prevent harmful consumption. These include capping the legal amount of THC allowed in all products and taxing marijuana based on the potency of THC in a product.
Freeman, T. P., Craft, S., Wilson, J., Stylianou, S., ElSohly, M., Di Forti, M., & Lynskey, M. T. (2021). Changes in delta-9-tetrahydrocannabinol (THC) and cannabidiol (CBD) concentrations in cannabis over time: systematic review and meta-analysis. Addiction (Abingdon, England), 116(5), 1000–1010. https://doi.org/10.1111/add.15253
 Freeman T. P., Hindocha C., Green S. F. (2019) Medicinal use of cannabis based products and cannabinoids. Bloomfield M. A. 365: l1141.
 Stuyt E. (2018). The Problem with the Current High Potency THC Marijuana from the Perspective of an Addiction Psychiatrist. Missouri medicine, 115(6), 482–486.
Petrilli, K., Ofori, S., Hines, L., Taylor, G., Adams, S., & Freeman, T. P. (2022). Association of cannabis potency with mental ill health and addiction: a systematic review. The lancet. Psychiatry, 9(9), 736–750. https://doi.org/10.1016/S2215-0366(22)00161-4
 NIDA. 2021, April 13. Is there a link between marijuana use and psychiatric disorders?. Retrieved from https://nida.nih.gov/publications/research-reports/marijuana/there-link-between-marijuana-use-psychiatric-disorders on 2023, January 12
NIDA. 2021, April 13. Is marijuana addictive?. Retrieved from https://nida.nih.gov/publications/research-reports/marijuana/marijuana-addictive on 2023, January 12
 Curran, H. V., Freeman, T. P., Mokrysz, C., Lewis, D. A., Morgan, C. J., & Parsons, L. H. (2016). Keep off the grass? Cannabis, cognition and addiction. Nature reviews. Neuroscience, 17(5), 293–306. https://doi.org/10.1038/nrn.2016.28