Cannabis – also known by a host of other names such as pot, weed, marijuana and Ganja – is a drug that comes from a plant (cannabis sativa). Cannabis use can affect our minds and bodies. Here we look at the link between cannabis and our mental and physical health.
How does cannabis work? Effects on the brain
Cannabis contains over 100 different chemicals called cannabinoids [1]. Some examples are cannabidiol (CBD) and Tetrahydrocannabinol (THC). THC is the main active ingredient in cannabis. Potent forms of cannabis (‘skunk’) have a greater effect due to the high levels of THC.
When smoked, cannabis will go into your bloodstream and will quickly be carried to your brain. Once there it will attach to your receptors, or the nerve endings in your body which respond to certain changes and stimuli. This results in your brain releasing certain neurotransmitters and hormones, which can affect your thoughts, feelings and behaviors [2]. Levels of dopamine – a neurotransmitter which plays an important role in pleasure and reward [3] – are thought to be affected by cannabis use. [4]
Cannabis can also be eaten – for example, baked into brownies or bought in the form of chocolate or gummy bears. When ‘edibles’ are consumed, cannabis will take longer to get into your bloodstream, travelling through your stomach and liver first. However, its effects are often more pronounced and last longer. Because edibles take longer to have an effect, and it’s more difficult to know the dosage of THC you’re consuming, it’s important to ‘start low and go slow’ if you decide to use cannabis in this way. [5]
Cannabis has both short and long term effects on our brains.
Recent marijuana use (within 24 hours) has an immediate impact on thinking, attention, memory, coordination, movement and time perception. [6]
Longer term, it is thought that developing brains in infants, young people, and adolescents are especially susceptible to the harmful effects of cannabis and THC. [7] Various pieces of research have linked cannabis use in expectant mothers with problems with attention, memory, problem-solving skills, and behavior in their children after birth. [8].
Using cannabis before the age 18 may affect how the brain builds connections for functions like attention, memory, and learning. These effects could last a long time, or even be permanent [9]. More research is needed to fully understand the implications of cannabis use in young people.
The impact of cannabis on the brain depends on many factors, including:
- Amount of THC in the cannabis
- How regularly it is used
- Age when first used
- Whether other substances (such as tobacco, alcohol and other drugs) are used at the same time
How does cannabis make you feel?
Cannabis is now legal in most US states for recreational or medicinal use, including alleviating nausea and sickness in chemotherapy patients. [10] However, cannabis should not be perceived as ‘safe’ to use. It can have both positive and negative effects on our minds and bodies, and this relationship is not yet fully understood.
When people refer to ‘getting high’, they are normally talking about some of the perceived benefits of using cannabis. These could include:
- Feeling more relaxed
- Feeling happier
- Talking more than usual
- Laughing more than usual
- Experiencing an altered or heightened perception of colors or sounds around us
Unfortunately, there are some downsides too, including some severe effects on our mental health [2]. The negative effects of weed range from mild, such as mood changes and increased anxiety, to severe, including visual or auditory hallucinations like seeing or hearing things that others can’t. Other reported effects include:
- Depersonalization – feeling outside of your own body
- Paranoia, delusion,and disorientation
- Loss of memory and concentration
- Slurred speech
Is cannabis addictive?
Estimates suggest around 3 in 10 marijuana users in the US have cannabis use disorder – defined as problematic cannabis use (abuse or dependence). [11] You’re more likely to become addicted if you start using it before the age of 18 or use it every day. You might find you build up a tolerance to cannabis if you use it regularly, meaning you need to consume more in order to get the same effect [2].
Those addicted to cannabis often report experiencing withdrawal symptoms when they don’t use it. These can include changes to our feelings, thoughts, and behaviors, such as:
- Irritability
- Restlessness
- Weight loss
- Appetite loss
- Cravings
- Nausea
- Mood swings
- Sleep problems
- Lacking motivation
- No longer enjoying life or the things you used to enjoy
Can cannabis cause mental health conditions?
UK research [12] has found a correlation between cannabis use and prevalence of mild, moderate, and severe mental health problems, such as depression, anxiety, and serious mental illness (SMI) – a category under which conditions like schizophrenia are classified.
Some US studies have linked cannabis use with suicidal thoughts and behaviors in certain demographics, including teens [13] and military veterans. [14]
Using cannabis – especially at high doses – can induce a temporary psychotic episode in some individuals, meaning that they lose touch with reality [15]. The association between cannabis use and psychosis or psychotic symptoms is possibly bidirectional. Meaning, people who use cannabis regularly are more likely to develop psychotic disorders than the general population, and experiencing psychosis increases your likelihood of using cannabis. Genetic factors could also play a role both in terms of likelihood of psychosis and cannabis use. [16]
Admissions data from the University of Colorado hospital in Denver [17] suggests that those who had ingested cannabis in the form of edibles were more likely to report heart problems and psychiatric symptoms, such as psychosis and anxiety, compared to those who had inhaled (smoked) cannabis. The study however is limited to one emergency room making it difficult to generalize to the wider population.
Although a link has been established between frequent cannabis use and mental health, the relationship is complicated, and we can’t say for certain that one causes the other. This is because people with mental health problems are more likely than the general population to use cannabis (sometimes known as ‘self-medicating’). [18] There are also a number of other contributory factors to poor mental health among cannabis users, including starting to use weed at an early age, using strong types of cannabis (with a high potency of THC), and the presence of any ‘genetic vulnerabilities’ (an increased risk of developing a mental health problem among those who have family members with a diagnosed mental health condition).
In addition, other factors that influence mental health—such as adverse childhood events (ACEs), trauma, and stress—also influence how likely someone is to use drugs, including cannabis. Given the multitude of factors involved, we need more research to better understand the relationship between cannabis and mental health.
Other long-term effects of cannabis use
Cannabis use can affect our physical health too.
Cancer
- Some research suggests it can help relieve some of the adverse side effects of undergoing cancer treatment (chemotherapy) such as nausea and vomiting. But other studies have established a link between cannabis use and testicular cancer, although more research is needed. For those who smoke cannabis with tobacco, there is an increased risk of lung cancer as associated with smoking more generally (tobacco or cigarettes). [19]
Heart
- Cannabis use can make the heart beat faster and increases blood pressure immediately after use.It could also lead to increased risk of stroke, heart disease and other vascular diseases.
- Most of the scientific research that has established a link between cannabis use and heart attacks and strokes has involved people who smoked marijuana (as opposed to other methods such as eating).
- Cannabis smoke also delivers many of the same substances found in tobacco smoke which are harmful to the lungs and cardiovascular system.It is therefore difficult to separate the effects of cannabis chemicals on the cardiovascular system from those caused by the irritants and other chemicals present in the smoke. [20]
Lungs
- Because cannabis is often smoked with tobacco, it poses the same risks to our lungs that smoking does. These risks include,harming lung tissue and causing scarring and damaging small blood vessels as well as increasing the risk of bronchitis, cough, and the production of mucus.
- At the moment, little is known about the extent to which there isa relationship between cannabis and respiratory conditions like emphysema. [21]
Quitting cannabis
If you want to cut down on your cannabis use, or quit altogether, it’s worth thinking about the reasons why you’re using cannabis, and what is making it difficult to stop.
If you’re smoking cannabis in a joint with tobacco you may become addicted to nicotine. Smoking tobacco increases your risk of associated diseases such as lung cancer, stroke, and heart disease. [22] It could be helpful to speak to someone about stopping smoking altogether. Nicotine is addictive so bear in mind that it can be difficult to stop. But remember, people can and do, so it’s worth persevering. Do ask for support, and don’t be disheartened if you can’t stop straight away.
Support for smoking cessation includes:
- Nicotine replacement therapies are available on prescription and help decrease nicotine cravings and withdrawal symptoms. Talk to your doctor or pharmacist about whether they could help.
- There are lots of resources to help with stopping smoking, including dealing with the physical cravings (medication) and helping support with any underlying mental disordersor emotional difficulties (counselling). [23]
If you’re using cannabis to help manage a mental health problem or emotional difficulties, it’s important to get help for your mental health. It’s often a combination of things that work best in managing a mental health problem. Treatment may involve a combination of psychiatric medication, talk therapy, exercise, and spending time with loved ones. A good place to start is by talking to your doctor or finding a therapist through MentalHealth.com.
- Rethink Mental Illness. (2019). How does cannabis affect my mental health? How Does Cannabis Affect My Mental Health? https://www.rethink.org/advice-and-information/about-mental-illness/learn-more-about-conditions/cannabis-and-mental-health/
- Juárez Olguín, H., Calderón Guzmán, D., Hernández García, E., & Barragán Mejía, G. (2016). The role of dopamine and its dysfunction as a consequence of oxidative stress. Oxidative Medicine and Cellular Longevity, 2016(1), 1–13. https://doi.org/10.1155/2016/9730467
- Bloomfield, M. A. P., Ashok, A. H., Volkow, N. D., & Howes, O. D. (2016). The effects of Δ9-tetrahydrocannabinol on the dopamine system. Nature, 539(7629), 369–377. https://doi.org/10.1038/nature20153
- Barrus, D., Capogrossi, K., Cates, S., Gourdet, C., Peiper, N., Novak, S., Lefever, T., & Wiley, J. (2016). Tasty THC: Promises and Challenges of Cannabis Edibles. https://doi.org/10.3768/rtipress.2016.op.0035.1611
- National Academies of Sciences, E., Division, H. and M., Practice, B. on P. H. and P. H., & Agenda, C. on the H. E. of M. A. E. R. and R. (2017, January 12). Preface. Www.ncbi.nlm.nih.gov; National Academies Press (US). https://www.ncbi.nlm.nih.gov/books/NBK425764/
- Batalla, A., Bhattacharyya, S., Yücel, M., Fusar-Poli, P., Crippa, J. A., Nogué, S., Torrens, M., Pujol, J., Farré, M., & Martin-Santos, R. (2013). Structural and Functional Imaging Studies in Chronic Cannabis Users: A Systematic Review of Adolescent and Adult Findings. PLoS ONE, 8(2), e55821. https://doi.org/10.1371/journal.pone.0055821
- Grewen, K., Salzwedel, A. P., & Gao, W. (2015). Functional Connectivity Disruption in Neonates with Prenatal Marijuana Exposure. Frontiers in Human Neuroscience, 9, 601. https://doi.org/10.3389/fnhum.2015.00601
- Meier, M. H., Caspi, A., Ambler, A., Harrington, H., Houts, R., Keefe, R. S. E., McDonald, K., Ward, A., Poulton, R., & Moffitt, T. E. (2012). Persistent cannabis users show neuropsychological decline from childhood to midlife. Proceedings of the National Academy of Sciences, 109(40), E2657–E2664. https://doi.org/10.1073/pnas.1206820109
- Gressler, L. E., Baltz, A. P., Costantino, R. C., Slejko, J. F., & Onukwugha, E. (2020). Exploring the Use of State Medical Cannabis Legislation as a Proxy for Medical Cannabis Use Among Patients Receiving Chemotherapy. Current Treatment Options in Oncology, 22(1). https://doi.org/10.1007/s11864-020-00803-2
- Keerthy, D., Chandan, J. S., Abramovaite, J., Gokhale, K. M., Bandyopadhyay, S., Day, E., Marwaha, S., Broome, M. R., Nirantharakumar, K., & Humpston, C. (2021). Associations between primary care recorded cannabis use and mental ill health in the UK: a population-based retrospective cohort study using UK primary care data. Psychological Medicine, 1–10. https://doi.org/10.1017/s003329172100386x
- Allan, N. P., Ashrafioun, L., Kolnogorova, K., Raines, A. M., Hoge, C. W., & Stecker, T. (2019). Interactive effects of PTSD and substance use on suicidal ideation and behavior in military personnel: Increased risk from marijuana use. Depression and Anxiety, 36(11), 1072–1079. https://doi.org/10.1002/da.22954
- National Institute of Mental Health. (2020). Understanding Psychosis. Www.nimh.nih.gov. https://www.nimh.nih.gov/health/publications/understanding-psychosis
- Gage, S. H. (2019). Cannabis and psychosis: triangulating the evidence. The Lancet Psychiatry, 6(5), 364–365. https://doi.org/10.1016/s2215-0366(19)30086-0
- Monte, A. A., Shelton, S. K., Mills, E., Saben, J., Hopkinson, A., Sonn, B., Devivo, M., Chang, T., Fox, J., Brevik, C., Williamson, K., & Abbott, D. (2019). Acute Illness Associated With Cannabis Use, by Route of Exposure: An Observational Study. Annals of Internal Medicine, 170(8), 531–537. https://doi.org/10.7326/M18-2809
- Rup, J., Freeman, T. P., Perlman, C., & Hammond, D. (2021). Cannabis and mental health: prevalence of use and modes of cannabis administration by mental health status. Addictive Behaviors, 121, 106991. https://doi.org/10.1016/j.addbeh.2021.106991
- CDC. (2021, October 29). CDC – fact sheet – health effects of cigarette smoking – smoking & tobacco use. Smoking and Tobacco Use; U.S. Department of Health & Human Services. https://www.cdc.gov/tobacco/data_statistics/fact_sheets/health_effects/effects_cig_smoking/index.htm
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Claire Bennett is a medical writer with 14+ years of experience with a (B.Sc.) degree in Psychology from the University of Sheffield.
Morgan Blair is a licensed therapist, writer and medical reviewer, holding a master’s degree in clinical mental health counseling from Northwestern University.
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