Is smoking weed bad for your health?

Question

Some people believe that smoking marijuana (without any tobacco) is harmful to your health and may cause problems. Examples of things I've heard weed supposedly causes:

• All the health problems of tobacco (cancer, strokes, etc)
• You get addicted to it and can't stop
• It fries your brain
• If you smoke too much you can die

I know for a fact that the last one is false, as the scientific consensus is that an overdose of marijuana in a human being is for all intents and purposes impossible. I'm not sure what "frying your brain" even means, and I don't know about the first two.

Has it been scientifically proven that weed is, or isn't, harmful?

Answer 1

It might be that smoking or ingesting marijuana has positive/nuetral effects on certain health issues and nuetral/negative effects on others. The consensus of studies are generally inconclusive in this regard.

For example, there are studies that say there is a 50% increase in the odds of suffering from schizophrenia after trying cannabis

Others that say:

1. "We hypothesized that there would be a positive association between marijuana use and lung cancer, and that the association would be more positive with heavier use," he said. "What we found instead was no association at all, and even a suggestion of some protective effect."

2. "Earlier work established that marijuana does contain cancer-causing chemicals as potentially harmful as those in tobacco, he said. However, marijuana also contains the chemical THC, which he said may kill aging cells and keep them from becoming cancerous." - Link to Washington Post Article

and more recently:

Moderate Marijuana Use Does Not Impair Lung Function, Study Finds

Other studies have been conducted on the specific interaction between THC and cancer cells. This study, conducted by the Journal of Clinical Investigation states that:

...THC can promote the autophagic death of human and mouse cancer cells and provides evidence that cannabinoid administration may be an effective therapeutic strategy for targeting human cancers.

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Again, I am not overlooking the potential health risks that have been proven to be associated with marijuana use, but I think it is a complex issue and media reports typically focus on potential negative health effects of marijuana use without mentioning potential positive health effects.

I think this graphic helps illustrates my point about the media reports:

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Answer 2

1. Weed can cause some health problems, but not greater than tobacco or alcohol. It all depends on quantity/quality and personal health. So for perfectly healthy persons occasional use may have no effect, but for persons with heart problems it can do real damage.
2. Can result in dependence, but less than amphetamines, tobacco or alcohol.
3. No.
4. There are no deaths recorded caused only by using cannabis. But there are deaths associated with usage of weed (car accidents, choking on vomit, etc.)

Advisory Council on the Misuse of Drugs(UK) states that:

• High use of cannabis is not associated with major health problems for individuals or society.

• Smoking cannabis may be more dangerous than smoking cigarettes because it has a higher concentration of carcinogens.

• Occasional use of cannabis is only rarely associated with significant problems in otherwise healthy individuals, with the main worry being impaired control of your movements. It can also disrupt the control of blood pressure and increase the risk of fainting. However, occasional use can pose significant dangers for those with heart and circulation disorders and for those with schizophrenia.

• Regular heavy use of cannabis can result in dependence but its addictive potential is far less than amphetamines, tobacco or alcohol.

• Cannabis impairs mental functions such as attention, memory and performance and so can be dangerous for drivers and those who operate heavy machinery but, unlike alcohol, it does not increase risk-taking behaviour.

• The birth weight of children whose pregnant mothers smoked joints might be lower than expected due to carbon monoxide in the smoke. They also run a small risk of minor birth defects.

• Cannabis is less harmful than other class B substances including amphetamines, barbiturates or codeine-like compounds.

Answer 3

There is some evidence that consumption of cannabis can cause shizophrenia in some people (see this BMJ editorial), the newest study about this connection claims

Cannabis use is a risk factor for the development of incident psychotic symptoms. Continued cannabis use might increase the risk for psychotic disorder by impacting on the persistence of symptoms.

Answer 4

Cannabis is generally pretty innocuous as far as psychoactive drugs go. It's not entirely without negative consequences, however. There seems to be reasonable evidence (mostly correlative, granted, but there are enough correlations to be worried) for memory deficits and for decreased reaction speed in the face of contradictory information.

(Linked-to studies picked almost at random from among a number that have similar findings.)

Answer 5

I’m bothered with the ‘you smoke cigarettes and you smoke weed, if cigarettes cause cancer weed does’ anti-science here. There are studies suggest the opposite, that smoking weed can reduce some forms of cancer. I’m not aware of a single study demonstrating that pot smokers who don’t ALSO smoke tobacco have any increased cancer rate.

Marijuana use and cancer incidence (California, United States). Sidney S, Quesenberry CP Jr, Friedman GD, Tekawa IS. Source Division of Research, Kaiser Permanente Medical Care Program, Oakland, California 94611-5714, USA. Abstract The purpose of this retrospective cohort study was to examine the relationship of marijuana use to cancer incidence. The study population consisted of 64,855 examinees in the Kaiser Permanente multiphasic health checkup in San Francisco and Oakland (California, United States), between 1979-85, aged 15 to 49 years, who completed self-administered questionnaires about smoking habits, including marijuana use. Follow-up for cancer incidence was conducted through 1993 (mean length 8.6 years). Compared with nonusers/experimenters (lifetime use of less than seven times), ever- and current use of marijuana were not associated with increased risk of cancer of all sites (relative risk [RR] = 0.9, 95 percent confidence interval [CI] = 0.7-12 for ever-use in men; RR = 1.0, CI = 0.8-1.1 in women) in analyses adjusted for sociodemographic factors, cigarette smoking, and alcohol use. Marijuana use also was not associated with tobacco-related cancers or with cancer of the following sites: colorectal, lung, melanoma, prostate, breast, cervix. Among nonsmokers of tobacco cigarettes, ever having used marijuana was associated with increased risk of prostate cancer (RR = 3.1, CI = 1.0-9.5) and nearly significantly increased risk of cervical cancer (RR = 1.4, CI = 1.0-2.1). We conclude that, in this relatively young study cohort, marijuana use and cancer were not associated in overall analyses, but that associations in nonsmokers of tobacco cigarettes suggested that marijuana use might affect certain site-specific cancer risks.

Cannabinoids in the treatment of cancer Amy Alexandera, Paul F. Smitha and Rhonda J. Rosengren , a, Abstract Cannabinoids, the active components of the hemp plant Cannabis sativa, along with their endogenous counterparts and synthetic derivatives, have elicited anti-cancer effects in many different in vitro and in vivo models of cancer. While the various cannabinoids have been examined in a variety of cancer models, recent studies have focused on the role of cannabinoid receptor agonists (both CB1 and CB2) in the treatment of estrogen receptor-negative breast cancer. This review will summarize the anti-cancer properties of the cannabinoids, discuss their potential mechanisms of action, as well as explore controversies surrounding the results. Keywords: Cannabinoids; JWH-133; CB1; CB2; MAPK

[The endocannabinoid system as a target for the development of new drugs for cancer therapy]. [Article in Italian] Bifulco M, Di Marzo V. Source Dipartimento di Scienze Farmaceutiche, Università di Salerno, Istituto di Endocrinologia ed Oncologia Sperimentale del CNR, Dipartimento di Biologia e Patologia Cellulare e Molecolare, Università Federico II, Napoli. maubiful@unina.it Abstract Studies on the main bioactive components of Cannabis sativa, the cannabinoids, and particularly delta 9-tetrahydrocannabinol (THC), led to the discovery of a new endogenous signalling system that controls several physiological and pathological conditions: the endocannabinoid system. This comprises the cannabinlid receptors, their endogenous agonists--the endocannabinoids--and proteins for endocannabinoid biosynthesis and inactivation. Recently, evidence has accumulated indicating that stimulation of cannabinoid receptors by either THC or the endocannabinoids influence the intracellular events controlling the proliferation and apoptosis of numerous types of cancer cells, thereby leading to anti-tumour effects both in vitro and in vivo. This evidence is reviewed here and suggests that future anti-cancer therapy might be developed from our knowledge of how the endocannabinoid system controls the growth and metastasis of malignant cells. PMID: 12723496 [PubMed - indexed for MEDLINE]