That's literally what the person you're replying to is asking for. They asked for Bloodwalker to provide studies showing that pot is bad for you since that is what was claimed. The burden of proof is on Bloodwalker to show that it has a negative effect on health. Zxcv asked for this proof, and since there aren't really any studies (that I'm aware of) that show any major negative effects of smoking marijuana (except for the expected danger of underage smoking, or driving under the influence), he/she got a bit cocky with it.

So I guess I'm wondering, what makes you think the burden of proof is on zxcv? They didn't make the original claim that pot is unhealthy. Since you didn't bother quoting a study either, I'll do the work for you. Here's a study that shows that long term pot use is not associated with any major physical health problems. The study actually found that people who smoke marijuana long term generally have slightly worse periodontal health, but also...

"Findings showed that cannabis use was associated with slightly better metabolic health (smaller waist circumference, lower body mass index, better lipid profiles, and improved glucose control)," the study determined. However, these associations were fairly small and by no means strong enough to recommend regular bong hits as a weight management strategy.

There you go. Very slightly better metabolic health, very slightly worse teeth. The study even said that participants had no decreased lung function over 12 years of heavy use.