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Medical Marijuana: Facts, Myths, and Dangers

Medical Marijuana—Facts, Myths, and Dangers

Medical marijuana helps many people around the world. While the promise shown by medical marijuana has lead to its increasing popularity, it has also lead to the spread of misinformation. We must clearly distinguish dangerous medical marijuana myths from science-based facts.

The Need for Clarity Regarding Medical Marijuana Myths

As the world continues to decriminalize and legalize cannabis, more people are being turned on to its potential benefits in treating diseases and reducing symptoms. As a result, more people need to know about the safety and efficacy of medical marijuana.

Cannabis and its active components, known as cannabinoids, have numerous applications.

The two most researched two cannabinoids are tetrahydrocannabinol (THC) and cannabidiol (CBD). THC causes intoxication, whereas CBD does not. Nonetheless, the two compounds share similar medical benefits and there is some evidence that suggests they are more effective when used together.[1]

As with any medicinal substances, there are also a number of risks associated with the use of cannabis. This article provides clarity regarding the evidence-based uses of cannabis and real risks, and also dispels some medical marijuana myths.

Scientifically Supported Uses of Medical Marijuana

Clinical trials have produced strong evidence for the efficacy of marijuana for treating a number of medical conditions.

Pain Management

Medical marijuana cannot effectively treat severe pain (such as post-surgical pain). However, evidence suggests that it helps to treat less serious, chronic pain. Cannabis helps manage neuropathic pain and chronic non-cancer, non-neuropathic pain.[2]

Cannabis is appealing as a pain-management medication because it presents fewer side effects and has lower addiction potential when compared to opioids. Access to medical marijuana tends to reduce the number of overall opioid prescriptions.[3] When used in conjunction with opioids, cannabis leads to greater pain relief and allows a reduction in the dosage of opioids.[4]

Managing Nausea and Vomiting Caused by Chemotherapy

Medical marijuana helps reduce the nausea and vomiting caused by chemotherapy treatments. The cannabinoids are more effective than some commonly-used antiemetic (anti-nausea) medications, and patients often prefer the use of cannabinoids over conventional medicines.[5]

Managing Multiple Sclerosis Symptoms

Strong evidence suggests that medical marijuana improves patient-reported spasticity symptoms in people with multiple sclerosis (MS). [6] Short-term use of orally-consumed cannabinoids seems to provide the most reliable improvement. Cannabis extracts also help treat muscle stiffness and have been shown to be twice as effective as a placebo. [7]

Reducing Seizures

Marijuana has been considered as a remedy for epilepsy for many years, but research has only recently shown it to be useful. Marijuana rich in CBD helps to reduce seizures in patients with the epileptic conditions known as Dravet syndrome and Lennox-Gastaut syndrome. CBD-rich cannabis extracts provide improvements without subjecting patients to the intoxicating side effects of THC.[8]

Questionable or Completely Unsupported Uses of Medical Marijuana

Medical marijuana research has produced limited or no evidence of its efficacy as a treatment for a number of conditions.

Managing Symptoms of Dementia and Related Conditions

Some people have suggested that CBD-rich cannabis extracts are effective for treating various dementia-related conditions, including Alzheimer’s and Parkinson’s. Currently, however, evidence is limited. CBD may suppress the causal factors contributing to Alzheimer’s,[9] but more research is needed to confirm the link.

Improving Short-Term Sleep in People with Chronic Conditions

Limited evidence suggests that cannabis helps to improve sleep quality in people struggling with multiple sclerosis, rheumatoid arthritis, peripheral neuropathic pain, and intractable cancer pain.[10]

Helping to Fight Symptoms of Anxiety

Cannabis and cannabinoids have an interesting relationship with anxiety. THC is known to both aggravate and soothe symptoms of anxiety in different populations.[11] CBD shows more potential for managing anxiety. In public speaking tests, CBD leads to significant decreases in anxiety, cognitive impairment, and discomfort.[12] Preclinical evidence also suggests that CBD can manage generalized anxiety disorder, panic disorder, social anxiety disorder, and other anxiety-related mental health disorders.[13]

Managing post-traumatic stress disorder

Medical marijuana research has investigated the efficacy of cannabis for reducing symptoms of post-traumatic stress disorder (PTSD), which has historically been very difficult to treat.

Research has shown that certain cannabinoids, namely THC and CBD, can mitigate some symptoms of PTSD such as reducing nightmare frequency.[14] Synthetic cannabinoids have been shown to improve sleep quality.[15] Unfortunately, research has found no evidence that THC improves other symptoms of PTSD.[16]

Managing Glaucoma Symptoms

Cannabinoids may reduce intraocular pressure,[17] which contributes to the development of glaucoma. Cannabis is being considered for future glaucoma treatments.[18]

Increased Appetite & Weight Gain in Chronically Ill People

Marijuana use increases appetite. For this reason, researchers consider it a possible treatment for weight loss associated with conditions like HIV, AIDS, and cancer.

Smoked marijuana leads to an increase in food intake by HIV patients.[19] However, repeated use of cannabis seems to result in developing a tolerance to these effects,[20] suggesting that it might not be useful as a long-term solution.

A long-standing result is that marijuana increases appetite in cancer patients.[21] However, side effects such as hallucinations and sedation can make this treatment unappealing, particularly to elderly patients.[22]

Conditions Often Made Worse by Medical Marijuana

Medical marijuana research has found some conditions that medical marijuana can actually aggravate. Unfortunately, persistent medical marijuana myths cause the public to believe that marijuana can effectively treat these conditions.

Psychosis and schizophrenia

Researchers are considering the use of CBD for treating psychosis.[23] Some evidence shows that CBD can help to reduce symptoms of schizophrenia.[24] However, other studies following similar procedures found no significant improvements.[25]

Conversely, cannabinoids such as THC are associated with an increased risk of psychosis.[26] The regular use of cannabis also contributes to the emergence of schizophrenia.[27]

Focus and cognitive function

Some evidence suggests that CBD can improve cognitive functioning in regular cannabis users.[28] This has led some to believe that the whole cannabis plant may help to improve overall cognitive ability.

However, the cognitive impairment caused by THC is among the most well-established effects of consuming cannabis. [29] THC also contributes to changes to brain structure[30] and memory loss.[31]

While research acknowledges the possibility that CBD might mitigate some of the undesirable cognitive side effects of THC,[32] more research is needed to determine the relationship between these cannabinoids and cognitive function.


Researchers studying CBD recognize that it may have some ability to help prevent addiction. It shows promise for limiting drug-seeking behavior[33] and may help reduce symptoms of anxiety—which is closely linked to substance use disorders.[34]

However, cannabis itself carries a serious risk of addiction. Approximately 9% of all marijuana users develop cannabis use disorder.[35] The risk of addiction is greater in youth, who are roughly 2-to-4 times more likely to develop cannabis use disorder than adults.[36]

Summary of Medical Marijuana Facts, Myths, and Areas of Uncertainty

Cannabis can be an effective treatment for a variety of ailments. However, it’s important to shed light on medical marijuana myths and to distinguish science-backed statements from speculation and fiction.

Strong evidence supports the use of medical marijuana or cannabis extracts for treating seizures, multiple sclerosis (MS) symptoms, chronic pain, and chemotherapy-induced nausea. Limited evidence suggests that cannabis or its extracts may help to improve symptoms of post-traumatic stress disorder (PTSD), dementia, glaucoma, anxiety, and insomnia. Sufficient evidence also indicates that cannabis can aggravate conditions including psychosis, addiction, and cognitive impairment.

As with any medicinal substance, distinguishing medical marijuana myths from evidence-based statements makes everyone safer by decreasing the likelihood of its use in potentially harmful or unhelpful contexts. However, the most important thing to remember is to always seek professional medical advice from a doctor or psychiatrist—never try to treat medical conditions or disease symptoms on your own.


[1] Allan, M. et al., (2018). Evidence for THC versus CBD in cannabinoids. Can Fam Physician

[2] (Banerjee) Banerjee, S., McCormack, C., (2019). Medical cannabis for the treatment of chronic pain: a review of clinical effectiveness and guidelines.  CADTH Rapid Response Report

[3] Grinspoon, P. (2019). Access to medical marijuana reduces opioid prescriptions. Harvard Health

[4] Lucas, P. (2012). Cannabis as an Adjunct to or Substitute for Opiates in the Treatment of Chronic Pain. Journal of Psychoactive Drugs, 44(2), 125–133. doi: 10.1080/02791072.2012.684624

[5] Tramer, M. R. (2001). Cannabinoids for control of chemotherapy induced nausea and vomiting: quantitative systematic. Bmj323(7303), 16–16. doi: 10.1136/bmj.323.7303.16

[6] Zajicek, J. P. (2005). Cannabinoids in multiple sclerosis (CAMS) study: safety and efficacy data for 12 months follow up. Journal of Neurology, Neurosurgery & Psychiatry, 76(12), 1664–1669. doi: 10.1136/jnnp.2005.070136

[7] Zajicek, J. P., Hobart, J. C., Slade, A., Barnes, D., & Mattison, P. G. (2012). MUltiple Sclerosis and Extract of Cannabis: Results of the MUSEC trial. Journal of Neurology, Neurosurgery & Psychiatry, 83(11), 1125-1132. doi:10.1136/jnnp-2012-302468

[8]  Perucca, E. (2017). Cannabinoids in the Treatment of Epilepsy: Hard Evidence at Last? Journal of Epilepsy Research, 7(2), 61-76. doi:10.14581/jer.17012

[9] Hee Kim, S., et al., (2019) A Review on Studies of Marijuana for Alzheimer’s Disease – Focusing on CBD, THC.

[10] Russo, B., et al. (2007) Cannabis, Pain, and Sleep: Lessons from Therapeutic Clinical Trials of Sativex®, a Cannabis-Based Medicine. ChemInform, vol. 38, no. 47, 2007, doi:10.1002/chin.200747254.

[11] Tambaro, S., & Bortolato, M. (2012). Cannabinoid-related Agents in the Treatment of Anxiety Disorders: Current Knowledge and Future Perspectives. Recent Patents on CNS Drug Discovery, 7(1), 25-40. doi:10.2174/157488912798842269

[12] Bergamaschi, M, et al.  (2011) Cannabidiol Reduces the Anxiety Induced by Simulated Public Speaking in Treatment-Naïve Social Phobia Patients. Neuropsychopharmacology, vol. 36, no. 6, 2011, pp. 1219–1226., doi:10.1038/npp.2011.6.

[13] Blessing, E. M., Steenkamp, M. M., Manzanares, J., & Marmar, C. R. (2015). Cannabidiol as a Potential Treatment for Anxiety Disorders. Neurotherapeutics, 12(4), 825-836. doi:10.1007/s13311-015-0387-1

[14] Roitman, P., Mechoulam, R., Cooper-Kazaz, R., & Shalev, A. (2014). Preliminary, Open-Label, Pilot Study of Add-On Oral Δ9-Tetrahydrocannabinol in Chronic Post-Traumatic Stress Disorder. Clinical Drug Investigation, 34(8), 587-591. doi:10.1007/s40261-014-0212-3

[15] Jetly, R., Heber, A., Fraser, G., & Boisvert, D. (2015). The efficacy of nabilone, a synthetic cannabinoid, in the treatment of PTSD-associated nightmares: A preliminary randomized, double-blind, placebo-controlled cross-over design study. Psychoneuroendocrinology, 51, 585–588. doi: 10.1016/j.psyneuen.2014.11.002

[16] Parker, L. (2018). Cannabinoids and the brain. Cambridge, MA: The MIT Press.

[17] Panahi, Y., Manayi, A., Nikan, M., & Vazirian, M. (2017). The arguments for and against cannabinoids application in glaucomatous retinopathy. Biomedicine & Pharmacotherapy, 86, 620–627. doi: 10.1016/j.biopha.2016.11.106

[18] Tomida, I. (2004). Cannabinoids and glaucoma. British Journal of Ophthalmology, 88(5), 708–713. doi: 10.1136/bjo.2003.032250

[19] Haney, M. (2002). Effects of smoked marijuana in healthy and HIV + marijuana smokers. J Clin Pharmacology.

[20] Bedi, G., Foltin, R. W., Gunderson, E. W., Rabkin, J., Hart, C. L., Comer, S. D., … Haney, M. (2010). Efficacy and tolerability of high-dose dronabinol maintenance in HIV-positive marijuana smokers: a controlled laboratory study. Psychopharmacology, 212(4), 675–686. doi: 10.1007/s00213-010-1995-4

[21] Voth, E. A. (1997). Medicinal Applications of Delta-9-Tetrahydrocannabinol and Marijuana. Annals of Internal Medicine, 126(10), 791. doi: 10.7326/0003-4819-126-10-199705150-00008

[22] Yeh, S.-S., Lovitt, S., & Schuster, M. W. (2007). Pharmacological Treatment of Geriatric Cachexia: Evidence and Safety in Perspective. Journal of the American Medical Directors Association, 8(6), 363–377. doi: 10.1016/j.jamda.2007.05.001

[23] Almeida, B. (2018). Cannabidiol in the Treatment of Psychosis – A review. doi: 10.26226/morressier.5a6ef3efd462b80290b58a05

[24] Mcguire, P., Robson, P., Cubala, W. J., Vasile, D., Morrison, P. D., Barron, R., … Wright, S. (2018). Cannabidiol (CBD) as an Adjunctive Therapy in Schizophrenia: A Multicenter Randomized Controlled Trial. American Journal of Psychiatry, 175(3), 225–231. doi: 10.1176/appi.ajp.2017.17030325

[25] Boggs, D. L., Surti, T., Gupta, A., Gupta, S., Niciu, M., Pittman, B., … Ranganathan, M. (2018). The effects of cannabidiol (CBD) on cognition and symptoms in outpatients with chronic schizophrenia a randomized placebo controlled trial. Psychopharmacology, 235(7), 1923–1932. doi: 10.1007/s00213-018-4885-9

[26] Hall, W., & Degenhardt, L. (2008). Cannabis use and the risk of developing a psychotic disorder. World Psychiatry, 7(2), 68–71. doi: 10.1002/j.2051-5545.2008.tb00158.x

[27] Almeida, B. (2018). Cannabidiol in the Treatment of Psychosis – A review. doi: 10.26226/morressier.5a6ef3efd462b80290b58a05

[28] Solowij, N., Broyd, S. J., Beale, C., Prick, J.-A., Greenwood, L.-M., Hell, H. V., … Yücel, M. (2018). Therapeutic Effects of Prolonged Cannabidiol Treatment on Psychological Symptoms and Cognitive Function in Regular Cannabis Users: A Pragmatic Open-Label Clinical Trial. Cannabis and Cannabinoid Research, 3(1), 21–34. doi: 10.1089/can.2017.0043

[29] Broyd, S. J., Hell, H. H. V., Beale, C., Yücel, M., & Solowij, N. (2016). Acute and Chronic Effects of Cannabinoids on Human Cognition—A Systematic Review. Biological Psychiatry, 79(7), 557–567. doi: 10.1016/j.biopsych.2015.12.002

[30] Lorenzetti, V., Solowij, N., & Yücel, M. (2016). The Role of Cannabinoids in Neuroanatomic Alterations in Cannabis Users. Biological Psychiatry, 79(7). doi: 10.1016/j.biopsych.2015.11.013

[31] Curran, V., Brignell, C., Fletcher, S., Middleton, P., & Henry, J. (2002). Cognitive and subjective dose-response effects of acute oral Δ 9 -tetrahydrocannabinol (THC) in infrequent cannabis users. Psychopharmacology, 164(1), 61–70. doi: 10.1007/s00213-002-1169-0

[32]Hudson, R., Renard, J., Norris, C., Rushlow, W. J., & Laviolette, S. R. (2019). Cannabidiol Counteracts the Psychotropic Side-Effects of Δ-9-Tetrahydrocannabinol in the Ventral Hippocampus through Bidirectional Control of ERK1–2 Phosphorylation. The Journal of Neuroscience, 39(44), 8762–8777. doi: 10.1523/jneurosci.0708-19.2019

[33] Hurd, Y. L., Yoon, M., Manini, A. F., Hernandez, S., Olmedo, R., Ostman, M., & Jutras-Aswad, D. (2015). Early Phase in the Development of Cannabidiol as a Treatment for Addiction: Opioid Relapse Takes Initial Center Stage. Neurotherapeutics, 12(4), 807–815. doi: 10.1007/s13311-015-0373-7

[34] Frances, R. J. (2008). Prevalence, Correlates, Disability, and Comorbidity of DSM-IV Drug Abuse and Dependence in the United States: Results From the National Epidemiologic Survey on Alcohol and Related Conditions. Yearbook of Psychiatry and Applied Mental Health, 2008, 76–78. doi: 10.1016/s0084-3970(08)70671-6

[35] Lopez-Quintero, C., Cobos, J. P. D. L., Hasin, D. S., Okuda, M., Wang, S., Grant, B. F., & Blanco, C. (2011). Probability and predictors of transition from first use to dependence on nicotine, alcohol, cannabis, and cocaine: Results of the National Epidemiologic Survey on Alcohol and Related Conditions (NESARC). Drug and Alcohol Dependence, 115(1-2), 120–130. doi: 10.1016/j.drugalcdep.2010.11.004

[36] Anthony, J. C., & Petronis, K. R. (1995). Early-onset drug use and risk of later drug problems. Drug and Alcohol Dependence, 40(1), 9–15. doi: 10.1016/0376-8716(95)01194-3

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