The effects of cannabis

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Medicinal and recreational Cannabis use is increasing worldwide, partially due to legislative changes in the United States, Europe and South America. The World Health Organization estimates that approximately 2.5% of the world’s population use cannabis. With the rapidly changing legal landscape surrounding cannabis, the number of people using marijuana is likely to increase.

Many patients receive cannabis for various reasons. Cannabinoids have a role in the brain’s control of movement and memory, as well as natural pain modulation. It is clear that cannabinoids can affect pain transmission and, specifically, that cannabinoids interact with the brain’s endogenous opioid system and may affect dopamine transmission and therefore efficient for Parkinson’s patients. Cannabinoids can be used as very effective anti-inflammatory, anti-convulsive, anti-seizures, too.

The effects of cannabis are caused by the chemical compounds in the plant, including cannabinoids, such as tetrahydrocannabinol (THC), which is psychoactive and one of more than 140 different cannabinoids present in the plant.

Tetrahydrocannabivarin (THCV) has also some psychoactive activity. At lower doses, THCV may act as an antagonist of the cannabinoid receptor type 1 (CB1). At higher doses, however, it can switch, behaving as a CB1 agonist, much like THC.

Cannabis has various psychological and physiological effects on the human body. Different plants of the genus Cannabis contain different and often unpredictable concentrations of THC and other cannabinoids and hundreds of other molecules (terpenes and flavonoids) that have a pharmacological effect.

Some clinical studies have proposed that CBD acts as a balancing force to regulate the strength of the psychoactive agent THC. CBD is also believed to regulate the body’s metabolism of THC by inactivating cytochrome P450, an important class of enzymes that metabolize drugs.

Cannabidiol (CBD) can alleviate the adverse effects of THC.

It is very important the method of consumption.

When smoked, the short-term effects of cannabis manifest within seconds and are fully apparent within a few minutes, typically lasting for 1–3 hours, varying by the person and the strain of cannabis. After oral ingestion of cannabis, the onset of effect is delayed relative to smoking, taking 30 minutes to 2 hours, but the duration is prolonged due to continued slow absorption.

When THC is ingested orally, it can produce stronger psychotropic effects than inhaled. THC is converted rapidly to 11-OH-THC, which is also pharmacologically active, so the drug effect outlasts measurable THC levels in blood.



The psychoactive effects of cannabis, known as a “high”, are subjective and can vary based on the person and the method of use.

Some effects may include:

  • a general alteration of conscious perception

  • euphoria

  • feelings of well-being

  • relaxation or stress reduction

  • increased sensuality

  • increased awareness of sensation

  • increased libido

  • increased creativity 

Somatic effects

Some of the short-term physical effects of cannabis use include:

  • increased heart rate

  • dry mouth

  • reddening of the eyes (congestion of the conjunctival blood vessels)

  • a reduction in intra-ocular pressure

  • muscle relaxation

  • a sensation of cold or hot hands and feet and / or flushed face.

Anxiety and panic attacks:

At high doses of THC patients can have anxiety and panic attacks that can result in increased heart rate and changes in blood pressure.

Several studies have indicated that smoking marijuana is associated with a dose dependent increase in heart rate[1],[2],[3]. Additionally, smoking marijuana decreases oxygen carrying capacity in the face of an increased oxygen demand. Aronow and Cassidy[4] demonstrated that among people with stable angina, smoking one marijuana cigarette decreases the time to angina with exercise by 48% compared with a 9% decrease in subjects smoking a marijuana placebo that did not contain delta-9-tetrahydrocannabinol.

A study[5]  found that marijuana use was associated with similar risk of receiving a coronary angiogram when compared to the control group, but marijuana-use patients were significantly less likely to undergo percutaneous coronary intervention; (PCI).

This suggests that these marijuana-use patients did not have significant coronary artery disease or acute plaque rupture as the inciting event for their acute myocardial infarctions (AMI).


Some patients have Short-term memory problems during consumption of cannabis.

Some patients with a family record of psychosis might have a psychosis attack but usually the presence of CBD reduces the effect of THC.

Cannabinoids are lipophilic (fat-soluble) compounds that are easily stored in fat, thus yielding a long elimination half-life relative to other recreational drugs.



[1] Bloom JW, Kaltenborn WT, Paoletti P, Camilli A, Lebowitz MD. Respiratory effects of non-tobacco cigarettes. Br Med J (Clin Res Ed). 1987; 295(6612):1516±8.

[2] Devlin RJ, Henry JA. Clinical review: Major consequences of illicit drug consumption. Crit Care. 2008;12(1):202. PMID: 18279535

[3] Sherrill DL, Krzyzanowski M, Bloom JW, Lebowitz MD. Respiratory effects of non-tobacco cigarettes: a longitudinal study in general population. Int J Epidemiol. 1991; 20(1):132±7. PMID: 2066211

[4] Aronow WS, Cassidy J. Effect of marihuana and placebo-marihuana smoking on angina pectoris. N Engl J Med. 1974; 291(2):65±7. PMID: 4599385


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