Quantity of smoke inhaled is several orders of magnitude smaller than with cigarettes. There's some evidence to suggest that, whether due to quantity or other factors, smoking marijuana casually does not substantially harm lung function[1].
Tobacco companies said the opposite of what their studies showed--so they lied.
Claiming that marijuana is typically smoked orders of magnitude less than cigarettes is not at all a lie but is truly one of the main reasons marijuana doesn't lead to the same lung cancer rates as cigarettes.
Back of the napkin math:
Imagine the average smoker smokes a pack of cigarettes a day. 20 cigarettes in a pack and 15 drags per cigarette = 300 drags of smoke per day.
A moderate (or even heavy) marijuana user smokes a bowl or two per day and takes ~4 hits per bowl = 8 drags a day.
Plus marijuana is not addictive like cigarettes so the number of casual marijuana users who can remain once-in-a-while partakers is much higher than with cigarettes. And if funds are tight it's easier for people to stop spending their money on marijuana than on cigarettes. Marijuana's cost on society is overall a lot lower than the societal cost of cigarettes.
Just for some perspective here because I'm not ashamed of myself...
Two bowls per day I'd consider light usage (less than a bowl a day I'd say is very light, or occasional). Heavy users are smoking over an ounce a week, which is greater than an eighth a day. That's quite a few more than two bowls.
At my height I was smoking between 8-12 king size spliffs per day. Though a spliff is mixed with tobacco.
I was a very heavy user, but I was also not that exceptional for the area (PDX).
I still smoke, even though it's likely bad for me. Like drinking, you don't do it for the positive health effects, you do it because it's fun, social, or you simply want to...
you're the cannabis equivalent of a 3 pack a day tobacco smoker. the very high end of extremely heavy usage. the average cannabis user is probably smoking like 1 joint per week, honestly. a daily user maybe smokes 1 joint per day. very few people have jobs where they can be stoned all day.
Do you have any facts to back this up? I just don't think the average marijuana user only uses a single joint in a week. I've known a lot of people who smoke and that amount seems off.
And a lot more people than you'd expect are stoned all day. You just can't tell because they're past the giggling munchies phase of smoking.
I really wish I had better data I could link to you. Just reporting my intuition based on personal experience, and knowing a lot of cannabis users. For obvious reasons, it's not so easy to find good methodically rigorous longitudinal studies of cannabis use.
It definitely is, but there are also compounds in marijuana that seem to inhibit cancers (citation needed). From memory, the result is that you can still get lung cancer, but the rate of it is much lower than would be expected.
[1]: https://www.scientificamerican.com/article/casual-marijuana-...