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Cannabis is the common name and genus for a few plants used around the world due to their psychoactive properties. Its major component, known as THC, possesses acute benefits but is subject to rapid tolerance. Additionally, nonpsychoactive components like CBD may have chronic benefits. While therapeutic, the plant is not a panacea.

Our evidence-based analysis on cannabis features 724 unique references to scientific papers.

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Summary of Cannabis

Primary information, health benefits, side effects, usage, and other important details

Cannabis is the common name for a few plants in the cannabis genus including sativa, indica, and ruderalis used for its psychoactive properties around the world. Cannabis has also been traditionally used to treat inflammatory disorders.

Today, cannabis is used as an adjuvant cancer therapy, meaning it is used alongside other drugs that treat cancer. Medical cannabis use can alleviate pain and increase appetite. It is also being investigated for its effect on inflammation and chronic disorders like rheumatoid arthritis.

Inhaling cannabis smoke increases diastolic blood pressure and heart rate, though this change is temporary. However, there are many case studies that note cannabis usage 30 – 60 minutes before heart attacks. Heart attacks can occur when people with an elevated risk for heart disease push their blood pressure and heart rate to dangerous levels. It may also interact with some pharmaceuticals, which could result in elevated blood pressure and a heart attack. Smoking cannabis has also been associated with bronchitis.

Cannabis and Δ9THC, or delta-9 tetrahydrocannabinol, are well researched because they act on the cannabinergic system in the body, which is actually namedcannabis after the plant. This system is regulated by two receptors, called cannabinoid receptor type 1 (CB1) and cannabinoid receptor type 2 (CB2). CB1 is responsible for most of the psychoactive effects of cannabis, and CB2 is responsible for many of the long-term benefits cannabis may provide for inflammation and related diseases.

Cannabis usage over a long period of time can cause tolerance, and subsequently withdrawal. Cannabis withdrawal is recognized by the Diagnostic and Statistical Manual of Mental Disorders (DSM-5). On a molecular level, cannabis tolerance occurs when the CB1 receptor is overstimulated and internalized, meaning absorbed by the cell. The CB1 receptor and the N-methyl-D-aspartate receptor (NMDA) receptor are linked when it comes to cannabis, so when CB1 signaling is inhibited, NMDA signaling is also hampered. This causes cannabis to be less effective for treating epilepsy and schizophrenia, though it also reduces the memory loss associated with cannabis use. Tolerance does not significantly affect the CB2 receptor, so cannabis may be effective for inflammatory disorders over a longer period of time.

Finally, high cannabidiol (CBD) products tend to be considered much different for therapeutic effects than are high Δ9THC products. Due to acting primarily on calcium channels known as TRPs, cannabidiol and other nonpsychoactive cannabinoids are thought to have therapeutic uses in the realms that Δ9THC fails (childhood epilepsy being the major one). While human evidence is lacking at the moment, there does appear to be reasonable evidence to suggest fairly potent therapeutic effects with high cannabidiol products.

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How to Take

Recommended dosage, active amounts, other details

Cannabis is usually inhaled to experience its psychoactive effects but can also be taken orally, sublingually (placed and held under the tongue), or via suppository. The route of consumption will dictate how quickly its effects will be felt with inhalation and suppository acting faster than sublingual or oral consumption.

The benefits and side-effects related to cannabis consumption will typically occur at doses large enough to cause a mild to moderate high. The most common dose range used in clinical trials is 2–5 mg per day (although this dose is typically concentrated THC).

Most side-effects of cannabis use are associated with frequency, not dosage. Using cannabis more than once a week might result in tolerance. Some people may need to restrict their usage to twice a month to avoid developing a tolerance.

Do not increase cannabis doses to overcome tolerance unless directed to do so by a medical professional.

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Human Effect Matrix

Unlocked for Examine members

The Human Effect Matrix summarizes human studies to tell you what effects Cannabis has on your body, how much evidence there is, and how strong these effects are.

Full details are available to Examine members.
Grade Level of Evidence
Robust research conducted with repeated double-blind clinical trials
Multiple studies where at least two are double-blind and placebo controlled
Single double-blind study or multiple cohort studies
Uncontrolled or observational studies only
Level of Evidence
? The amount of high quality evidence. The more evidence, the more we can trust the results.
Outcome Magnitude of effect
? The direction and size of the supplement's impact on each outcome. Some supplements can have an increasing effect, others have a decreasing effect, and others have no effect.
Consistency of research results
? Scientific research does not always agree. HIGH or VERY HIGH means that most of the scientific research agrees.
- See all 9 studies
A single use in a new user will increase diastolic blood pressure (no real influence on systolic), and this is subject to tolerance. Heavy users will not experience this acute increase anymore and may instead have a decrease in diastolic blood pressure.
- See all 3 studies
Both increases and decreases seem to have been reported over the whole brain, and it seems that in people who do not experience orthostatic hypotension from cannabis it is generally an increase; blood flow to the ACC in particular is increased following THC, but this becomes a decrease during tolerance.
- See all 10 studies
Similar to the diastolic blood pressure, heart rate modifications are subject to tolerance. New users may experience a reduced heart rate yet increased cardiac output, and heart rate during light exercise may be increased, with chronic users becoming tolerant to these effects.
grade-b Minor Very High See all 3 studies
Acute usage can reduce motor control and fine coordination, but this appears to be an effect that can be subject to tolerance (with tolerant users not seeing any difference following usage of cannabis).
grade-b Minor Very High See all 4 studies
There appears to be a reduction in pain associated with the dose of cannabis which confers psychoactive effects.
grade-b Minor High See all 4 studies
While cognitive symptoms have not yet been found to be treated with cannabis usage, physical symptoms and some parameters secondary to them (fatigue, energy, sleep quality) may be benefited with cannabis usage.
grade-c Notable - See study
The dose and time which confer psychoactive effects are associated with reported of relaxation to a larger degree than control.
grade-c Minor Very High See 2 studies
It seems that submaximal (light) aerobic exercise performance is not influenced much, but when aerobic exercise is carried to fatigue cannabis usage seems to be associated with less endurance relative to control.
grade-c Minor - See study
Dizziness has been reported as a side-effect specifically in users who experience orthostatic hypotension from cannabis; no major influence on dizziness otherwise.
grade-c Minor - See study
An increase in ghrelin has been noted with cannabis usage, likely playing a role in the increase in appetite.
grade-c Minor - See study
In a secondary data analysis on subjects with multiple sclerosis, it seems the side effect of incontinence may be reduced with cannabis usage.
grade-c Minor - See study
An increase in leptin has once been noted with usage of cannabis.
grade-c Minor Very High See all 3 studies
While smoking per se is seen as negative, infusions of THC enhance lung function and acute usage of cannabis as joints seem to confer more benefit to lung function than drawbacks.
grade-c Minor - See study
A decrease in serum peptide YY has been noted with cannabis usage, thought to be tied into its interactions with appetite.
grade-c Minor - See study
A reduction in reaction time has been noted in acute users of cannabis relative to control. While not directly tested, it is thought that this is attenuated during tolerance.
grade-c Minor - See study
Secondary to some benefits to physical symptoms in the treatment of multiple sclerosis, sleep quality was noted to be increased relative to placebo.
grade-c Minor Very High See all 3 studies
While not affecting all users, some new users may experience symptoms of orthostatic hypotension associated with a global decrease of blood flow to the brain (rather than the expected increase)
grade-c Minor Moderate See 2 studies
Acute working memory is decreased in new users of cannabis while under the influence, but during cannabis tolerance this hindering effect does not appear to persist.
grade-c - Very High See 2 studies
Tolerant users do not experience any attention reduction when inhaling cannabis.
grade-c - - See study
Despite alterations in cardiac output and diastolic blood pressure, acute usage of cannabis does not appear to influence the flow of blood relative to control.
grade-c - - See study
No significant influence on body temperature.
grade-c - - See study
When used during multiple sclerosis, a general battery of cognitive function does not appear to be greatly influenced (positive or negative) with cannabis therapy.
grade-c - Very High See all 3 studies
Depression as a symptom of multiple sclerosis does not appear to be significantly affected by cannabis therapy.
grade-c - Very High See all 4 studies
Mixed evidence in regards to physical and mental fatigue in the usage of cannabis for multiple sclerosis, with more studies suggesting the benefits are not statistically significant.
grade-c - - See study
Short term cannabis usage does not influence circulating insulin concentrations.
grade-c - Very High See 2 studies
Irritability as a side effect of multiple sclerosis does not appear to be significantly affected by cannabis therapy.
grade-c - - See study
Overall memory formation does not appear to be significantly affected by usage of cannabis.
grade-c - - See study
Acute inhalation of cannabis failed to modify grip strength when tested compared to control.
grade-d Notable Very High See all 3 studies
Inhalation of cannabis is able to reduce intraocular blood pressure quite significantly, leading to it being useful in instances of glaucoma.
grade-d Minor - See study
In hospitalized subjects chronic THC has been noted to increase weight; it should be noted this information differs from epidemiological studies on non-hospitalized subjects (either no change or a decrease in weight being observed).
grade-d - - See study
grade-d - - See study
Breathing rate does not appear to be inherently altered with usage of cannabis.
grade-d - - See study
There does not appear to be a significant influence of cannabis on urinary cortisol.
grade-d - - See study
grade-d - - See study
grade-d - - See 2 studies
grade-d - - See study
Despite a reduction in endurance (cycling until voluntary failure) the measured VO2 max between groups did not differ.
grade-d - - See study
During treatment of glaucoma with THC, visual acuity did not appear to be hindered.

Studies Excluded from Consideration

Note: Studies included in the HEM include all methods of administration except injections. Some benefits may be unique to oral supplementation (brownies) or inhalation (joints), and the commentary section will elucidate these differences if present

  • Used injections exclusively[1][2]

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Frequently Asked Questions and Articles on Cannabis

The science behind munchies: cannabis and your appetite
Tetrahydrocannabinol (THC), a cannabinoid in cannabis, can bind the cannabinoid receptor type 1 (CB1) and thus promote overeating and weight gain. This effect, detrimental to most people, can prove beneficial under certain medical conditions, such as cancer and HIV-associated wasting syndrome.

Things to Note

Primary Function:

Also Known As

Weed, Medical Marijuana, Marihuana, dope, ganja, hashish, Dronabinol (medical THC), Cannabis indica, Cannabis sativa, Marijuana

Do Not Confuse With

Hemp Protein (same plant, but this term tends to refer to a food product without THC)

Goes Well With

  • COX2 inhibitors (may reduce memory deficits associated with cannabis)

Caution Notice

Cannabis has a variable legal status depending on region, and may be illegal (to varying degrees) in your region if not for medicinal purposes.

Known drug and enzyme interactions.

  • Cannabis is highly psychoactive via both an oral and inhaled route

  • Cannabis can acutely reduce motor control and attention (and should not be inhaled prior to operating heavy machinery)

  • Cannabis is known to interact with many enzymes of drug metabolism of which include CYP3A4 and CYP2C19; see pharmacokinetic section for more information

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