Does smoking weed cause lung cancer, and is weed smoke worse than cigarette smoke? This covers what lab chemists found in the smoke, how people inhale joints, the Los Angeles and pooled case-control studies that found no link, the Swedish and New Zealand studies that suggest one for heavy use, why the studies disagree, what weed does to lung function and airways, what is known about vaporizers and the 2019 vaping lung injury outbreak, and whether THC kills cancer cells.
The full answer
Does smoking weed cause lung cancer?
Does smoking weed cause lung cancer? The big studies haven't shown that it does, but they haven't ruled it out for heavy, long-term smokers either. The smoke carries many of the same harmful chemicals as tobacco smoke. I'm Justin Hartfield, and I've been selling cannabis for twenty-five years. The answer depends on who has been studied and what else they were smoking.
Is weed smoke worse than cigarette smoke?
Is weed smoke worse than cigarette smoke? In some ways it is. Chemists at Health Canada machine-smoked joints and cigarettes rolled the same way. Weed smoke had up to twenty times as much ammonia and three to five times as much hydrogen cyanide and nitric oxide, but less of some cancer-causing hydrocarbons in the smoke you inhale. In 2020, another team identified a hundred and ten compounds in weed smoke known to cause cancer, mutations or other harm, against a hundred and seventy-three in tobacco smoke.
In 1988 at UCLA, fifteen men took bigger, deeper puffs from joints and held them four times as long, and they took in about three times as much tar as from a filtered cigarette of similar size. Then again, regular weed smokers usually smoke far fewer joints than cigarette smokers smoke cigarettes.
Is there a link between weed and lung cancer?
Is there a link between weed and lung cancer? A big Los Angeles study found none. It interviewed about twelve hundred people with cancers of the lung, mouth, throat or esophagus and about a thousand neighbors without cancer. Once cigarettes were accounted for, people who had smoked sixty joint-years or more, say two joints a day for thirty years, had no higher odds of lung cancer than people who had smoked none. A case-control study starts with people who already have cancer and asks what they smoked, and critics noted that only about four in ten of the cancer patients took part.
A 2015 analysis pooled six such studies from the US, Canada, Britain and New Zealand, with over two thousand lung cancer patients. People who had smoked the equivalent of at least a joint a day for a year had about the same odds of lung cancer as lighter users and non-users, including among people who had never smoked tobacco. The authors still wrote that a risk from heavy use can't be ruled out.
Can heavy weed smoking cause lung cancer?
Can heavy weed smoking cause lung cancer? Two studies say it might. In Sweden, about forty-nine thousand young men were asked about cannabis when they were drafted in 1969 and 1970, then tracked until 2009. Those who said at the draft that they had used it more than fifty times had about twice the risk of lung cancer, after adjusting for tobacco. This cohort followed people forward, but it asked about cannabis and tobacco only once, at eighteen to twenty.
New Zealanders rarely mix tobacco into joints. In 2008, a study there of seventy-nine people with lung cancer, all fifty-five or younger, and three hundred and twenty-four without it found the odds rose eight percent for every joint-year. People past ten and a half joint-years had five point seven times the odds, though with so few cases, the true figure could be anywhere from one and a half to over twenty.
Why do the studies disagree?
Why do the studies disagree? Mostly because of tobacco and small numbers. In the pooled data, eighty-six percent of regular weed smokers also smoked tobacco, against sixty-four percent of everyone else. In Britain and North Africa, tobacco often goes into the joint itself. Very few people in these studies had smoked a lot of weed for a long time, so the pooled authors called their estimates imprecise at high exposure. And cancer patients may have under-reported their use, which would hide a link.
Does smoking weed damage your lungs?
Does smoking weed damage your lungs? Light smoking doesn't seem to hurt lung function. A US study tested the lungs of five thousand one hundred and fifteen young adults in four cities over twenty years. Most smoked weed lightly, two or three times a month, and at low levels their lung capacity was, if anything, slightly higher. Past about ten joint-years that edge flattened out, and in people smoking more than twenty times a month, the air they could blow out in one second started to fall.
It does irritate your airways. In a 2018 meta-analysis, people who smoked weed were about twice as likely to have a cough and almost four times as likely to bring up phlegm, though the evidence was rated low-strength. Quitting seems to clear it. A UCLA team followed two hundred and ninety-nine people for about ten years, and those who quit weed or tobacco were no more likely to have chronic bronchitis than people who had never smoked.
Is vaping weed safer than smoking?
Is vaping weed safer than smoking? Heating flower without burning it may be easier on the airways, but the evidence is thin. In a 2007 online survey of six thousand eight hundred and eighty-three cannabis users, recruited through drug-law reform groups, sixty-six percent of the hundred and fifty-two who mostly used a vaporizer reported no breathing symptoms, against fifty-six percent of the others. After allowing for age, sex, cigarettes and how much they used, the vaporizer users had about forty percent of the odds of reporting symptoms. A survey like that can't show that the vaporizer made the difference, and the lead author declared ties to cannabis-law reform groups.
Vaping THC in e-cigarette devices is a different story. By February 2020, two thousand eight hundred and seven Americans had been hospitalized or died in the 2019 lung injury outbreak, including sixty-eight deaths, and of the patients with data on what they used, eighty-two percent reported THC products. A substance called vitamin E acetate turned up in the lung fluid of forty-eight of fifty-one patients and none of the ninety-nine healthy people tested, and the CDC linked most cases to THC vaping products from informal sources like friends and dealers.
Does THC kill cancer cells?
Does THC kill cancer cells? Nobody has shown that in people. In mice and cells, it has held lung tumors back. In 1975, THC slowed the growth of lung tumors in mice and helped them live longer. In 2008, a Harvard team found THC slowed the growth and spread of human lung cancer cells, in dishes and in mice, and noted that in other lab work THC has sped tumors up or slowed them down, depending on the cancer. I found no human trial of THC against lung cancer.
The whole film is on my site, linked below. Next: Can you get a contact high?
What the studies show
Every claim in this answer, the study behind it, who was studied, and who paid for the research. “None listed” means the paper names no funder.
