The Health Effects of Cannabis – What's Inside Report? - Sweedsy The Health Effects of Cannabis – What's Inside Report? - Sweedsy
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The Health Effects of Cannabis – What’s Inside Report?

The National Academies - Report on Cannabis

A comprehensive report “The Health Effects of Cannabis and Cannabinoids” released by the National Academy of Sciences sparked a whole spectrum of emotions around the nation. Cannabis advocates happily point at its conclusion that cannabis indeed possesses therapeutic value. Opponents worry about car incidents, potential memory problems, and underage use.

But the report states one thing very clear – we need more research. Let’s take a brief look at the paper and find out what we know about cannabis:

Brief Overview

Who did the report?

The National Academies of Science, Engineering, and Medicine.

It’s a private NGO established in 1863 to advise the nation on scientific matters. It’s considered to be one of the gold standard institutions of science.

The organization has already conducted a review of cannabis. In 1999, right after the legalization of medical marijuana in California, the White House Office of National Drug Control Policy asked the Institute of Medicine to review the scientific evidence regarding health risks and benefits of cannabis. The organization dug into the data, and surprisingly, concluded that cannabis could have beneficial effects for patients.

What did they do?

They put together the follow-up report to look what the science has discovered in the past 18 years regarding the therapeutic value of cannabis.

The organization reviewed more than 10,000 research articles and reached nearly 100 conclusions. Each particular research conclusion was graded according to one of five “levels of evidence”:

  • Conclusive
  • Substantial
  • Moderate
  • Limited
  • No/Insufficient Evidence.

N.B.: The committee focused exclusively on the human studies and didn’t consider basic research conducted using animal models. 

Based on this classification and analysis, the committee found three medical application for cannabis use supported by conclusive evidence:

  • Nausea and vomiting associated with cancer chemotherapy
  • Chronic pain in adults
  • Spasticity in multiple sclerosis.

What To Keep In Mind

What to keep in mind

Two sorts of issues to think about while reading:

The study of cannabis has big barriers

Research clearly emphasizes that we do not know quite much about marijuana and tries to elaborate why. Here are four main obstacles:

  • Specific regulatory barriers (cannabis is still Schedule I drug, remember?) affect the advancement of research on cannabis;
  • Researchers have significant problems to obtain cannabis products they need to understand the health effects of human cannabis consumption;
  • There is not enough money to support research efforts;
  • Scientists need to improve research methodologies and develop standardization for gathering conclusive evidence for the short- and long-term health effects of cannabis.

We all agree that cannabis should be more accessible for research. However, such conclusions contradict the decision of the federal government to keep marijuana as a Schedule I substance.

The study of cannabis has significant caveats

  1. The focus on human studies made finding correlational and prevented us from revealing cause-and-effect sequence. It means that the committee did not attempt to evaluate whether cannabis use caused a particular health outcome or whether cannabis use and the outcome were associated for some other reason.
  2. Human studies often rely on self-reporting. All the conclusion about the effects of cannabis are based on the assumption that subjects of the studies were accurately reporting their consumption.
  3. The committee decided not to consider basic research. It’s understandable because in this case, it would take forever to review tens of thousands of research abstracts. However, basic research allows us to look closer at the mechanism of action and establish cause-and-effect relationships. It also gives us a valuable inside into the outcomes of human clinical research. The decision to avoid basic research made a huge knowledge gap in the report.



Therapeutic Effects

  • Oral cannabinoids are effective in treating chemotherapy-induced nausea and vomiting in adults.
  • Adults with chronic pain are more likely to experience clinically significant levels of pain reduction when treated with cannabis or cannabinoids.
  • Oral cannabinoids provide improvement for adults with MS-related spasticity.

These effects have been widely known for some time and now are claimed to be robust and supported by evidence deemed “conclusive” by the committee. Note the second point; it is crucial in fighting the opioid epidemic in the country.

Cardiometabolic Risks

  • The evidence is unclear about the association of cannabis use with heart attack/stroke/diabetes.

Just a friendly reminder: people with heart issues should be extremely careful. Through CB1 receptors in the brain, THC can cause an acute increase in pulse and blood pressure.


  • Evidence suggests that smoking cannabis does not increase the risk of lung, head, or neck cancers in adults.
  • There’s limited evidence for an association between cannabis use and one particular subtype of testicular cancer.
  • There’s minimal evidence that parental cannabis use during pregnancy is associated with greater cancer risk in children.

Keep in mind that these conclusions are based on finding (or failing to find) statistical associations between cannabis use and a particular type of cancer. Studies like these require controlling for confounding variable (for example, tobacco smoking) and interpreting of the results should heavily depend on it. The association between cannabis use and one subtype of testicular cancer is deemed limited because the studies suffered from:

  • Self-reporting;
  • Low response rates;
  • Lack of controlling for confounding variable.

Respiratory Disease

  • Smoking cannabis regularly is associated with chronic coughing and phlegm production.
  • Quitting smoking is likely to reduce these symptoms.
  • It’s unclear if cannabis use is associated with other respiratory problems (e.g. asthma, general lung function).

Instead of smoking, switch to vaping. It helps to save you from heavy coughing and other respiratory complications.


  • There’s a general lack of data on how cannabis-based therapies affect the human immune system.
  • There is insufficient data on the overall effects of cannabis on immune system competence.
  • There is limited evidence suggesting that cannabis smoke exposure has anti-inflammatory effects.
  • There is insufficient evidence to support an association between cannabis use and adverse immune effects in HIV patients.

Based on the reviewed abstracts, the authors concluded that limited or lack of evidence exists. If we would look at the basic research, we find plenty of useful data. For example, we are aware that THC is a more potent anti-inflammatory than aspirin or hydrocortisone. We also know that the endocannabinoid system plays a significant role in regulating the immune’s system inflammatory response. That’s why it would be good to consider both basic and human studies.

Prenatal, Perinatal, and Neonatal Exposure

  • Smoking cannabis during pregnancy is associated with lower birth weights.
  • The relationship between smoking during pregnancy and other outcomes is unclear.

PSA: Don’t smoke anything if you’re pregnant. Studies suggest that non-cannabinoid byproducts of combustion (including carbon monoxide) can impair fetal growth.

Problem Use

  • Using cannabis more frequently and starting at a younger age are associated with developing problem cannabis use.

We talk about cannabis use disorder here. Cannabis is not as powerful in habit-forming as alcohol, nicotine, or opioids, but it is still possible. If you have trouble taking a break, or you experience withdrawal symptoms, then you have a habit. Frequent cannabis use and early start put you at risk.

Abuse of Other Substances

  • Cannabis use is likely to increase the risk of developing the dependence on a substance other than cannabis.

This one is tricky. The committee brings these three statements in the chapter of the full report:

  1. There is limited evidence for an association between cannabis use and the initiation of tobacco use.
  2. There’s limited evidence for cannabis use affecting the rates and patterns of use of other illicit substances.
  3. There is moderate evidence for a statistical association between cannabis use and the development of dependence for other substances, including alcohol, tobacco, and other illicit drugs.

It is pretty confusing. First, we are being told about limited evidence for an association between changes in patterns of use of tobacco or other illicit substances. Then, we are suddenly told that the evidence for such association is moderate. Development of dependence is itself a change in the pattern of usage. Also, most of the studies still rest on self-reporting without sufficient biological data that could give us a clue regarding predisposition towards the development of a substance abuse.

Until we have no answers to question how to separate substance’s use and establish a stable cause-and-effect relationship regarding abuse pattern, we cannot simply jump from limited evidence to moderate. Probably, this section should receive more attention.

Effects on Injury and Death

  • Using cannabis before driving increases the risk of being in a motor vehicle accident.
  • In states with legal cannabis, there’s an increase in unintentional cannabis overdose injuries in children.
  • There is no clear relationship between cannabis use and mortality or occupational injury.

It is common sense. Avoid driving under the influence of any psychoactive substance. Be careful and keep marijuana products out of children’s reach. Remember that edibles pose a threat to any unsuspecting individual who may mistakenly consume a terribly large amount of THC and have undesirable effects.

Once again – you cannot die from a cannabis overdose. Also, in the states with legal weed, people feel better and don’t skip the work or come there stoned.

Psychosocial Effects

  • Recent cannabis use (within the last 24 hours) impairs cognition (memory, attention).
  • A limited number of studies suggest there are such cognitive impairments in people who have stopped cannabis use.
  • Adolescent use is associated with impairments in subsequent academic achievement and other social outcomes.

THC intoxication leads to impairments in cognition, but there is limited evidence that such impairments persist after people stop consuming cannabis. Childhood and adolescence use should be restricted and avoided due to the critical periods of nervous system development.

Mental Health

  • Cannabis use can increase the risk of developing schizophrenia.
  • Individuals with schizophrenia and a history of cannabis use may show better performance on learning and memory tasks.
  • Cannabis use does not appear to increase the likelihood of depression, anxiety, or PTSD.
  • In individuals with bipolar disorder, near daily cannabis use may worsen symptoms.
  • Heavy cannabis users are more likely to report thoughts of suicide.
  • Regular cannabis use increases the risk for social anxiety disorder.

Points one and two may seem to contradict each other. However, let us get more specific. In box 12-1, titled “Co-Morbidity in Substance Abuse and Mental Illness,” gives us some clarification:

  1. Substance use may be a potential risk factor for developing mental health disorders.
  2. Mental illness may be a potential risk factor for developing a substance abuse disorder.
  3. An overlap in predisposing risk factors (e.g., genetic vulnerability, environment) may contribute to the development of both substance abuse and a mental health disorder.


The relationship between mental health and substance abuse is difficult and heavily dependent on each other. Mental health can affect a pattern of abuse, while abuse itself can bring underlying mental issues. Other, unexpected variables can affect both:

Although the precise explanation is still unclear, it is reasonable to assume that co-morbidity between substance abuse and mental health disorders may occur due to a mixture of proposed scenarios. With this context in mind, however, it is important to note that the issue of co-morbidity directly affects the ability to determine causality and/or directionality in associations between substance use and mental health outcomes. This is a complex issue, one that certainly warrants further investigation.



The report looks deeply into human health and how cannabis can potentially affect it. It is a titanic job to get this volume of data reviewed. It would be even bigger if basic research would be involved.

The committee’s choice not to dig into basic research has its flaws. A large proportion of human studies is based on self-reported data that is correlational in nature. A selection of the language and phrasing brings unnecessary ambiguity.

The primary outcome is that we need more quality research. This report concludes that the existing barriers and insufficient funding prevent advancement of current scientific efforts. However, the biggest obstacle is a designation of cannabis to Schedule I list. Rescheduling or removing the plant from this list will give us more valuable insight into how cannabis really works and which benefits it has.

This article has been written based on a brilliant review made by Nick Jikomes at Leafly. If you need more in-depth information, please, take a look at the original review.


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