What are the medical effects of cannabis?

Cannabis is a historic, multidimensional and sometimes controversial plant. Its versatility and usefulness have propelled cannabis into all kinds of industries and products, particularly in the medical field. Its therapeutic use has been studied for several centuries, and modern clinical studies tend to prove the medical effects of cannabis on numerous pathologies.

What you need to know about cannabis

Cannabis is made up of different active ingredients. The best known are cannabinoids with over 120 elements. Visit tetrahydrocannabinol (THC) and the cannabidiol (CBD) are the two cannabinoids most present in the Cannabis plant and the most widely studied. THC is responsible for the «high» effect» that many people associate with cannabis, while CBD is a non-intoxicating, non-euphoric component that you may have already seen in oils, candies, drinks or medicines.

Cannabis owes its medical effect to its action on the endocannabinoid system, a network of receptors in our body that regulates most of the body's major functions, such as appetite, pain, anxiety and sleep.

Are there any cannabis medicines available in France?

If the medical marijuana is not yet legal in France, the Agence Nationale de Sécurité du Médicament (ANSM) has approved several medicines containing cannabinoids :

• Epidiolex, which contains a purified form of cannabis-derived CBD, has been approved for the treatment of seizures associated with Lennox-Gastaut syndrome or Dravet syndrome, two rare and severe forms of epilepsy.
• Sativex, which contains equivalent levels of cannabis-derived THC and CBD, and is recommended for spasticity in multiple sclerosis.
• Marinol, which contain dronabinol (synthetic THC), used to treat nausea and vomiting caused by cancer chemotherapy. Dronabinol is also used to treat loss of appetite and weight loss in people with HIV/AIDS.

Experimenting with therapeutic cannabis has been taking place in France since 2021 and is due to open in 2025 with the «generalization» of medical cannabis.

Are cannabis or cannabinoids useful for treating health problems?

Cannabinoid-containing medicines may be useful in treating certain rare forms of epilepsy, nausea and vomiting associated with cancer chemotherapy, and loss of appetite and weight associated with HIV/AIDS. In addition, some data suggest modest benefits from cannabis or cannabinoids for chronic pain and the symptoms of multiple sclerosis. Research into cannabis or cannabinoids for other pathologies is still in its infancy.

The following sections summarize research on cannabis or cannabinoids for specific health conditions, without being exhaustive.

Cannabis and pain

Research has been carried out into the effects of cannabis or cannabinoids on chronic pain, particularly neuropathic pain (pain associated with nerve damage).

A 2018 review examined 47 studies (4,743 participants) of cannabis or cannabinoids for various types of chronic pain other than cancer pain and found evidence of a slight benefit. Twenty-nine percent of those taking cannabis or cannabinoids saw their pain decrease by 30 %, compared with 26 % of those taking a placebo (inactive substance). The difference may be too small to be significant for patients. Adverse events (side effects) were more frequent in people taking cannabis/cannabinoids than in those taking placebos.

A 2018 review of 16 studies of cannabis-based medicines for neuropathic pain, most of which tested Sativex, found low- to moderate-quality evidence that these medicines produced better pain relief than placebos. However, the data could not be considered reliable because the studies involved small numbers of people and could be biased. People taking cannabis-based medicines were more likely than those taking placebos to drop out of the studies because of’side effects of cannabis.

A 2015 review of 28 cannabinoid studies (2,454 participants) in which chronic pain was assessed revealed that the studies generally showed improvements in pain measures in people taking cannabinoids, but that these improvements did not reach statistical significance in most studies. However, the average number of patients reporting at least a 30 % reduction in pain was higher with cannabinoids than with placebo.

Help reduce opioid use

Animal studies show that administering THC at the same time as opioids can help control pain with a smaller dose of opioids.

A 2017 review looked at studies of people given cannabinoids alongside opioids to treat pain. The aim of these studies was to determine whether cannabinoids could provide pain control with a smaller amount of opioids. There were 9 studies (750 participants in total), 3 of which (642 participants) used a high-quality study design in which participants were randomly assigned to receive cannabinoids or placebo. Results were inconsistent, and none of the high-quality studies indicated that cannabinoids could lead to a reduction in opioid use.

Researchers examined statistical data on groups of people to determine whether access to medical cannabis is linked to changes in opioid use or changes in opioid-associated harm. The results were contradictory.

In U.S. states with medical cannabis laws, prescription rates for opioids and all drugs that cannabis could replace are lower among Medicare beneficiaries. However, data from a national survey (not limited to Medicare beneficiaries) showed that patients using medical cannabis were more likely than non-users to report taking prescription medication.

An analysis of data from 1999 to 2010 indicated that US states with medical cannabis laws had lower mortality rates for opioid analgesic overdoses, but when a similar analysis was extended to 2017, it showed higher mortality rates for this type of overdose.

An analysis of survey data from 2004 to 2014 showed that the adoption of medical cannabis laws was not associated with a decrease in the use of prescription opioids for non-medical purposes. Thus, people with access to medical cannabis do not appear to substitute for prescription opioids.

Anxiety and cannabis

A small body of evidence from human studies suggests that cannabis or the cannabinoids could help reduce anxiety. A study of 24 people with social anxiety disorder showed that they were less anxious in a simulated public speaking test after taking CBD than after taking a placebo. Four studies have suggested that cannabinoids may be useful in combating anxiety in chronic pain sufferers; the study participants did not necessarily suffer from anxiety disorders.

Epilepsy and cannabis

Cannabinoids, principally CBD, have been studied for the treatment of seizures associated with forms of epilepsy that are difficult to control with other drugs. L’Epidiolex (oral CBD) is approved in Europe for the treatment of seizures associated with two epileptic encephalopathies: Lennox-Gastaut syndrome and Dravet syndrome. Cannabinoids have not been sufficiently researched in other, more common forms of epilepsy to draw any conclusions as to their usefulness in these cases.

Glaucoma

Glaucoma is a group of diseases that can damage the eye's optic nerve, leading to vision loss and blindness. Early treatment can often prevent severe vision loss. Lowering the pressure in the eye can slow the progression of the disease.

Studies carried out in the 1970s and 1980s showed that cannabis or cannabis-derived substances could reduce eye pressure, but not as effectively as treatments already in use. One of the limitations of cannabis-based products is that they only act on eye pressure for a short period.

A recent animal study showed that CBD, applied directly to the eye, can cause an undesirable increase in eye pressure.

HIV/AIDS symptoms

Involuntary weight loss can be a problem for people living with HIV/AIDS. In 1992, the FDA approved the cannabinoid dronabinol for the treatment of appetite loss associated with weight loss in people with HIV/AIDS. This approval was based primarily on a 139-person study evaluating the effects of dronabinol on appetite and weight changes.

There have been a few other studies of cannabis or cannabinoids for appetite and weight loss in people with HIV/AIDS, but they were short and included only a small number of people, and their results may have been biased. Overall, the clinical evidence that cannabis and cannabinoids are beneficial for people with HIV/AIDS are limited but widespread among patients.

Inflammatory bowel diseases

Inflammatory bowel disease refers to a group of conditions in which the digestive tract becomes inflamed. Ulcerative colitis and Crohn's disease are the most common forms. Symptoms can include abdominal pain, diarrhea, loss of appetite, weight loss and fever. Symptoms can range from mild to severe, and can come and go, sometimes disappearing for months or years, then reappearing.

A 2018 review examined 3 studies (93 participants in total) that compared smoked cannabis or cannabis oil with placebos in people with active Crohn's disease. There was no difference between the cannabis/cannabis oil group and the placebo group in terms of clinical remission of the disease. Some people who took cannabis or cannabis oil saw their symptoms improve, but others experienced undesirable side effects. It is unclear whether the potential benefits of cannabis or cannabis oil outweigh the potential drawbacks.

A 2018 review examined 2 studies (92 participants) that compared smoked cannabis or CBD capsules to placebos in people with active ulcerative colitis. In the CBD study, there was no difference between the two groups in terms of clinical remission, but people taking CBD had more side effects. In the smoked cannabis study, a measure of disease activity was lower after 8 weeks in the cannabis group; no information on side effects was reported.

Irritable bowel syndrome

Irritable bowel syndrome (IBS) is defined as repeated abdominal pain accompanied by changes in bowel transit (diarrhea, constipation or both). It is one of a group of functional disorders of the gastrointestinal (GI) tract linked to the way the brain and intestine work together.

Although there is interest in the use of cannabis and cannabinoids to treat symptoms of irritable bowel syndrome, little research has been conducted on their use in humans. It is therefore not known whether cannabis or cannabinoids can be useful.

Movement disorders due to Tourette's syndrome

A 2015 review of two small placebo-controlled studies with 36 participants suggests that synthetic THC capsules may be associated with a significant improvement in tic severity in patients with Tourette syndrome.

Multiple sclerosis

Several cannabis/cannabinoid preparations have been studied for multiple sclerosis symptoms, including synthetic THC, Sativex and smoked cannabis.

An analysis of 17 studies of various cannabinoid preparations involving 3,161 participants showed that cannabinoids led to a slight improvement in spasticity (as assessed by the patient), pain and bladder problems in people with multiple sclerosis, but that cannabinoids did not significantly improve spasticity when measured using objective tests.

A review of 6 placebo-controlled clinical trials with a total of 1,134 participants concluded that cannabinoids (nabiximols, dronabinol and THC/CBD) were associated with greater mean improvement on the Ashworth scale for spasticity in multiple sclerosis patients compared with placebo, although this did not reach statistical significance.

The evidence-based guidelines published in 2014 by the’American Academy of Neurology concluded that nabiximols is probably effective in improving subjective symptoms of spasticity, probably ineffective in reducing objective measures of spasticity or urinary incontinence, and possibly ineffective in reducing multiple sclerosis-related tremor. Based on two small studies, the guidelines concluded that there is insufficient data to assess the effects of smoked cannabis in people with multiple sclerosis.

A 2010 analysis of 3 studies (666 participants) of nabiximols in people with multiple sclerosis and spasticity found that nabiximols reduced subjective spasticity, usually within 3 weeks, and that around a third of people receiving nabiximols in addition to another treatment would have at least a 30 percent improvement in spasticity. Nabiximol appears to be reasonably safe.

Nausea and vomiting associated with cancer chemotherapy

A 2015 review of 23 studies (1,326 participants) of cannabinoids to treat nausea and vomiting associated with cancer chemotherapy found that they were more useful than placebo and similar in efficacy to other drugs used for this purpose. However, side effects such as dizziness or drowsiness were more frequent in people taking cannabinoid-based drugs.

Research on dronabinol and nabilone in the treatment of cancer chemotherapy-related nausea and vomiting was conducted primarily in the 1980s and 1990s, and reflects the types of chemotherapy treatments and anti-nausea drug choices available then rather than now.

Post-traumatic stress disorder (PTSD)

Some post-traumatic stress sufferers have used cannabis or cannabis-based products in an attempt to alleviate their symptoms and believe it can help, but little research has been conducted to determine whether this is actually helpful.

In a very small study (10 people), the cannabinoid nabilone proved more effective than a placebo in relieving PTSD-related nightmares.

Observational studies (studies that collected data on PTSD sufferers who chose for themselves whether or not to use cannabis) have not provided clear evidence on the usefulness or harmfulness of cannabis for PTSD symptoms.

Sleep problems

Numerous studies on cannabis or cannabinoids in people suffering from health problems (such as multiple sclerosis, PTSD or chronic pain) have examined the effects of cannabis and cannabinoids. effects of cannabis on sleepl. People taking cannabis or cannabinoids have often been found to improve sleep quality, reduce sleep disturbances or shorten the time it takes to fall asleep. However, it is not known whether cannabis-based products have a direct effect on sleep, or whether people sleep better because the symptoms of their illness have improved. The effects of cannabis and cannabinoids on sleep problems in people without other illnesses are uncertain.

Are cannabis and cannabinoids safe?

Cannabis and cannabinoid safety has given rise to a number of concerns :

• Cannabis use has been associated with an increased risk of road accidents compared with sober driving, particularly among neo-consumers.
• Cannabis smoking during pregnancy is generally not recommended
• Some people who use cannabis for medical purposes develop a cannabis use disorder, manifested by symptoms such as craving, withdrawal, lack of control and negative effects on personal and professional responsibilities.
• Some long-term users of high doses of cannabis have developed a condition involving severe and recurrent vomiting, known as’cannabinoid hyperemesis
• Cases of contamination of cannabis/cannabinoid products by micro-organisms, pesticides or other substances have been reported.
• Some cannabis and cannabinoid products contain quantities of cannabinoids very different from those indicated on the label.

The medical use of cannabis requires all the caution normally associated with the use of medication. Patients should be accompanied by a physician throughout their course of treatment, who will know best whether a patient belongs to a specific group at increased risk of cannabis use. Consideration should be given to the ratio needed for the pathology, and the route of administration and initial dose that are safest for the patient.

When initiating cannabis, a low dose and slow titration method should be used. After initiation, it is essential to monitor adverse effects and drug interactions. Treatment plans should be adjusted to mitigate any potential problems or risks.

Just as there is a need for further research into the efficacy of medical cannabis, it is equally important to assess safety in order to reduce the risks associated with its use. There is a great need for greater efforts to evaluate safety factors regarding the use of medical cannabis with a wide range of conditions.

Can CBD be harmful?

Unlike Epidiolex, over-the-counter CBD products may contain more or less CBD than indicated on the label.

The CBD can have side effects, These include reduced alertness, mood swings, decreased appetite and gastrointestinal symptoms such as diarrhea. CBD may also produce psychotic effects or cognitive impairment in people who regularly use THC. In addition, CBD use has been associated with liver damage, male reproductive disorders and interactions with other drugs.

Some side effects, such as diarrhea, drowsiness, liver function test abnormalities and drug interactions, appear to be due to CBD itself rather than contaminants in CBD products; these have been observed in some people who participated in studies of Epidiolex prior to its approval as a drug.