What You Should Know: The Pros and Cons of Medical Marijuana

Last Updated on June 26, 2022 by Laura Turner

What You Should Know is an ongoing series covering a range of informational topics relevant to current and future healthcare professionals.
The numbers alone make it a significant issue: as of 2015, 23 states and the District of Columbia have legalized the use of medical marijuana – and 9 more states are currently working on legislation to do the same. Two more states – Washington and Colorado – have gone so far as to legalize its recreational use. It is likely, therefore, that medical students today will feel the effects of medical marijuana use when they go into practice for themselves.
Medical – and recreational – marijuana use is a complex issue with medical, political, and social implications. Below are evidence-based arguments for and against this use to give student doctors the opportunity to understand the finer points of this controversy.
The Arguments for Marijuana Use
Proponents of the medical use of marijuana do indeed have some clinical justification on their side. Though clinical studies have been scanty, research has been done that makes a compelling argument for the efficacy of marijuana as treatment for a variety of diseases and conditions, including pain uncontrolled by more conventional measures and glaucoma.
Pain Control
No examination of medical marijuana would be complete without a discussion of pain. Pain control, especially for complex and chronic disease processes like cancer and cirrhosis, is one of the most common reasons patients seek and are prescribed marijuana. Earlier this year, the Journal of the American Medical Association published a paper entitled “Medical Marijuana for the Treatment of Chronic Pain and Other Medical and Psychological Issues: a Clinical Review”, a detailed meta-analysis of clinical studies on this topic. They found that there was strong clinical evidence to support prescribed marijuana for conditions such as chronic, complex pain (including cancer pain), neuropathic pain and multiple sclerosis-related spasticity. It also commented, however, that for other clinical uses (such as post-chemotherapy nausea and vomiting) the evidence of marijuana’s efficacy is not so clear and that more research should be done on this particular issues.
American proponents of medical marijuana often bring up Canada as an example of the success of its use. It is true that in Canada, medical marijuana in the form of oral medications and even smoked cannabis is prescribed for pain control related to a variety of conditions. Even so, this medical use is tightly controlled and recommendations published in the Canadian Family Physician last year outlined the “do’s and don’ts” of smoked cannabis use for purposes of analgesia. According to the article, marijuana can be used in patients:
· Who have severe neuropathic or complex pain
· Who have not responded to pharmacological cannabis (i.e. oral medications containing cannabinoids) or traditional analgesics
However, the authors recommend that doctors use it with caution in patients:
· With past history of use of tobacco or other substances
· Are at an increased risk for heart disease
· Have a history of mood or anxiety disorders
· Are currently taking high doses of opioid analgesics
Furthermore, this use is contraindicated for patients:
· Under the age of 25
· With a history of psychosis
· With a history of cardiovascular or respiratory disease
· With current substance abuse issues
· Who are pregnant or who want to become pregnant
It is important to note that, even if the medical recommendations have been satisfied, this is far from a free-for-all and use of smoked marijuana for medical purposes is tightly controlled by Canadian law under the Marijuana for Medical Purposes Regulations (MMPR). In order to legally smoke marijuana for medical purposes, a patient must have the support of his/her health care provider and must purchase the marijuana from government-certified producers who in turn must meet high standards for quality and safety. The patient is only allowed to possess 30 times the prescribed daily limit (in other words, a month’s supply) of marijuana and that total itself is limited to no more than 150 grams.
In short, the consensus seems to be that while marijuana can help with certain types of complex, chronic pain, it should be used with caution and even in Canada, where it has been legalized for therapeutic use, this use is still tightly controlled.
Glaucoma is another condition proponents of medical marijuana use to strengthen their arguments that cannabis should have its place in the American pharmacopeia. There are multiple studies that confirm that cannabis can in fact decrease inter-ocular pressure (IOP), the underlying cause of glaucoma. One theory is that cannabinoids are able to lower IOP by lowering blood pressure generally; another theory states that they act on ciliary body cannabinoid receptors and lower aqueous humor production. Either way, studies have shown that on average, cannabis use can decreased IOP by an average of 25% — but that this effect only lasts for 3-4 hours and that the length of the effect is depending upon the dosage. However, many physicians are still leery of this treatment options due to concerns that cannabinoid use has serious drawbacks, such as the risk for dependence and withdrawal issues if the therapy is stopped.
Cannabis for glaucoma treatment can be oral or intravenous or can be smoked. However, while these routes most easily can decrease IOP, they also carry the largest risk for adverse side effects as opposed to eye drops which have few or no side effects. In the past, experiments with cannabinoid-containing drops have proven disappointing, but research is underway – armed with new knowledge of ocular cannabinoid receptors and the endocannabinoid system – to try to develop drops which will effectively lower IOP without risk of dependence or withdrawal. If this research is successful, it will likely make many physicians more comfortable prescribing such drops for their glaucoma patients.
Recreational Use
It is important to note that, to date, no clinical studies have been conducted on the health benefits of recreational marijuana use.
The Arguments Against Marijuana Use
Opponents of marijuana use also have strong clinical evidence to back up their beliefs – particularly in regards to recreational use. Most of the opposition to legalized marijuana for either medical or recreational purposes is based upon, unsurprisingly, the risk of adverse effects of marijuana use (particularly in the long term), negative outcomes for those who use marijuana as teens and even adverse effects when used for specific conditions such as Post Traumatic Stress Disorder (PTSD).
Health Effects of Long-Term Marijuana Use
One of the strongest arguments against use of marijuana is its adverse health effects, especially if used in the long term. In 2014, researchers conducted a meta-analysis of epidemiological studies done on the adverse effects of marijuana usage. What they found was clinical evidence to support the assertions that marijuana causes or contributes to:
· Cannabis dependence
· Increased risk that individual will use tobacco or street drugs
· Chronic bronchitis due to a compromised respiratory system
· Exacerbation of symptoms in cardiac disease
· Cognitive impairment, including to memory, learning and attention functions
· Poor academic performance
· Psychosis signs and symptoms such as delusions, hallucinations and disordered thinking
· Psychotic diagnoses like schizophrenia
· Exacerbation of manic depression
· Increased risk of suicide for teens and young adults.
Adverse Effects for Teen Usage
Opponents point out the possibility that legalization will “normalize” marijuana use and that as a result the number of young people and teens who use it for recreational reasons will grow. Last year in the journal Lancet Psychology, researchers of a paper entitled “Young Adult Sequelae of Adolescent Cannabis Use”, using data from three large, longitudinal studies from Australia and New Zealand, looked at use of marijuana before the age of 17 against 7 different important adult outcomes, including:
· High school completion
· The achievement of a university degree
· Cannabis dependence
· Use of street drugs
· Suicide attempts
· Depression
· Welfare dependence
When reporting these findings, researchers noted “We found clear and consistent associations…between the frequency of adolescent marijuana use and all adverse young adult outcomes.”
Poor Outcomes for PTSD Patients
In wake of the fact that many states have legalized use of marijuana for use by those suffering from PTSD, researchers conducted a longitudinal, observational study to evaluate the effects of marijuana use on those suffering from this disorder. This study looked at a large group of veterans, all of whom had been officially diagnosed with PTSD and divided them into four groups: 1) those who had never used marijuana, 2) those who had used marijuana upon admission but not after being discharged, 3) those who used at admission and after discharge and 4) those who began to use marijuana after being discharged. Upon analysis, it was found that groups 3 and 4, who had higher rates of marijuana usage, were significantly associated with worse PTSD outcomes, more violent behavior and a higher risk for alcohol and drug use compared to groups 1 and 2, who had lower rates of usage. However, it should be pointed out that this study in and of itself cannot definitively prove that it was marijuana which caused the increase in violence or if those with an increased propensity for violence were more likely to turn to marijuana usage.
And the Answer Is…
There likely is no good answer to this problem. Marijuana has clinically usefully properties for a number of important and serious conditions – and it has an equally well-proven potential for adverse effects such as dependence, poor life outcomes and an increased risk for suicide attempts and depression. In short, it should be handled carefully, and prescribed only when a physician understands the risks and benefits and weighs them carefully for each individual patient. One thing which allows doctors to do this is good education and knowledge of the clinical uses of marijuana – education that is sometimes lacking among practitioners.
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Hall, W. and Degenhalt, L. The Adverse Health Effects of Chronic Cannabis Use. Drug Testing
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Hill, K.P. Medical Marijuana for Treatment of Chronic Pain and Other Medical and
Psychological Problems: a Clinical Review. Journal of the American Medical
Association. 2015. 313(24) 2474-2483
Kahan, M. Prescribed Smoked Marijuana for Chronic Non-cancer Pain: Preliminary
Recommendations. Canadian Family Physician. 2014. 60(12) 1083-1090
Marihuana for Medical Purposes Regulation. Health Canada. 2015
Silas, E. et. al. Young Adult Sequelae of Adolescent Cannabis Use: an Integrative Analysis.
Lancet Psychology. 2014. 1(4) 286-293
Williamson, et. al. Marijuana Use is Associated with Worse Outcomes in Symptom Severity and
Violent Behavior in Patients with PTSD. Journal of Clinical Psychiatry. 2013. 76(9)
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