As someone who smoked it heavily for around 10 years (don't anymore) I know it can have negative effects. I witnessed them in myself and in the people around me at the time.

I'm pro-legalisation myself, but can't help roll my eyes at these 'potheads' that give the case for legalisation a bad name.

I don't argue this claim—I don't have any evidence either way—but nor do I regard it as self-evident. An honest, not rhetorical or leading, question: why should inhaling smoke be bad when inhaling, say, ordinary air isn't? Is it the heat? Particulates?

EDIT: Thanks for the excellent responses! (The detailed discussions below are far more interesting than my question, I think.) To be clear (since I am "submitting too fast" to reply to comments below), lest I sound like some kind of denier, when I say "I don't have any evidence either way", I mean literally that—just that I haven't bothered to get any, not that there isn't any.

"Ordinary air" is bad for your lungs when it's full of dust, soot, or other particulates. Smog is bad for you. So is smoke. So is pretty much anything else you might breath that includes particulates. Your lungs can handle it in small amounts but it's never good for them and long term exposure can be really bad for them.

The heat probably isn't great for your lungs either. But I doubt it's a significant factor.

http://berkeleyearth.org/wp-content/uploads/2015/08/China-Ai...

From this, various writers have attempted to make some extrapolations along the lines of "one day in Beijing is equivalent to smoking X cigarettes", where X ranges from 1/6 to 40. There are compelling arguments for both 1/6 and 40, despite those numbers seeming so different. Generally, the 1/6 figure comes from measuring the exact volume of dangerous substances inhaled, and the 40 figure comes from the premise that air pollution is significantly more damaging than tar from cigarettes and thus it takes much less of it to have the same effect as tar from 40 cigarettes. Regardless, the bottom line is that sometimes even ordinary air is not good for you.

Anyway, your observation that air in Beijing, etc., is polluted from smoke works towards my point, not against it.

Sam Harris had a decent presentation about it here: https://www.samharris.org/blog/item/the-fireplace-delusion

EDIT: This is just wood smoke I guess - You are asking about generic "smoke". I apologize for not addressing your question fully.

To the contrary, this is my favourite response (even though I don't have the religious response in defence of wood smoke that Sam Harris hopes to provoke). Thanks!

You haven't seen evidence that smoke inhalation is a hazard with both acute and long-term harms?

Try this: http://scholar.google.com/scholar?q=%22smoke+inhalation%22+p...

And I'm not the only one. I've lived with and been friends with quite a few long-term 'potheads'. Some, but not all of them, were also part of this 'weed culture'. I'd say at least half of them wanted to quit, tried to quit, but often didn't manage, for years on end.

Now, I think that's actually pretty decent all in all, considering 'my crowd', and it's nothing like what I've seen alcohol do! But it's still significant enough to be a little bit careful around pot. I'm all for legalization, but let's not pretend there are no risks!

Cannabis has been a Schedule 1 drug for decades, which makes it, according to the DEA's own definition, a drug "with no currently accepted medical use and a high potential for abuse."

It's only in the past couple of years that there's been any sort of serious talk about potential health benefits. Marijuana use and sale was first banned in 1937, and when that ban was later declared unconstitutional, the Controlled Substances Act of 1970 created the drug scheduling system and placed it in the "most dangerous" category.

Next year will mark the 80th anniversary of the original 1937 ban, so it seems hard to claim that the prevailing "Marijuana talk" of our time has focused on the health benefits, rather than the dangers. The reason there's been a small but constant discourse on the health benefits of cannabis over the past eight decades is that the current laws and the official DEA stance are clearly overzealous.

It's as if soft drinks were outlawed, and our government declared that they were as bad for your health as heroin. In truth, if you are a sufficiently heavy "daily drinker" of sugar water, you will develop a severe chemical dependence, and eventually wind up with type 2 diabetes, which will permanently damage your health and certainly shorten your lifespan. However, there's nothing wrong with having a root beer every now and then.

So if soft drinks had been illegal for the past 80 years because they had "no currently accepted medical use and a high potential for abuse" (which is true), you'd definitely be hearing some determined voices pointing out that there were some potential health benefits of sugar and water.

This is the number one stereotype of marijuana users, but I implore you to not lump all of us into that group. There exists a large portion of users that respect intelligence and try to lead interesting lives.

A big problem is that cannabis can make you feel totally OK with whatever you are currently doing, when otherwise you may feel bored and become motivated to do something else. Mix this with the fact that regular marijuana use probably won't destroy your life (it's simply not a hard drug), and you get people that float through existence feeling fine but then one day realize years have gone by and they forgot to develop unique skills or an interesting personality.

However, many people figure this out before it's too late and make sure that getting high goes hand-in-hand with doing something interesting. i.e. smoke and then create art, music, or software. For the people who don't realize this, well... the cold truth is that many people aren't smart or talented to begin with and maybe need some alleviation from the more painful aspects of the human condition. I believe weed is a better solution for this than hard drugs, Rx pills, or everyone's favorite toxin: alcohol.

Last of all I want to say that smoke is clearly carcinogenic, but there have been recent studies suggesting things that people would have thought crazy only 10-20 years ago:

http://www.cancer.gov/about-cancer/treatment/cam/hp/cannabis...

The other reason being the gradually mounting paranoia eventually culminating in what I can only describe as a paranoid anxiety attack.

The day that happened I quit.

I'm pro-legalisation but I abused it and ruined it for myself. Many others do too, all the while espousing its complete lack of drawbacks, which I find irritating.

You should re-phrase this as: "the people I know who publicly advertise the fact that they smoke pot".

In my experience, there are a lot of marijuana users who are otherwise extremely normal people (and even sometimes on the exceptional end of normal). But given the legal status of marijuana, an ambitious middle-aged professional with a young family who also smokes a couple times a month is unlikely to publicly advertise the fact.

Because you (presumably) don't smoke, those people are extremely unlikely to confide in you about this particular subject.

A good counter example is someone I know who didn't start until around age 25, only indulges occasionally (so it isn't an addiction), and has very high cognitive ability (currently making 6 figures in the financial industry).

That said, I personally don't feel comfortable indulging in something chronically that has such pronounced effect on my mental abilities. Even if it has no long-term physical consequences, the habit (and what comes with it: junk food, junk tv, lethargy, etc.) itself can't be ideal.

Perhaps it would work if I didn't have access to the internet and/or lived in a more nature-like area. Or perhaps it would work if my lifestyle was already different. I don't know. But as it is, if I smoke I become either couch-locked or jittery and paranoid.

I think individual differences matter a great deal, and you're right in pointing that out.

That said, the vast majority of regular pot smokers I know are more similar to me than they are to you, so based on that I think the negative bias is at least somewhat justified. I'd never tell someone not to smoke, I wouldn't judge chronic smokers no matter their lifestyle. But I've warned every one of my siblings and those curious about it to keep an eye out for how they respond to the stuff. It's nowhere near as potentially dangerous as alcohol, I think, but it's also not quite like picking up a coffee habit.

(I do have to confirm that I would occasionally get a burst of 'creativity' in particular when coding on purely-fun side-projects! Doing so was enjoyable and funny albeit not always very productive. I miss that sometimes.)