As usual, more and higher-quality data would help elucidate the source of the protective effects.
> The National Academies of Sciences, Engineering, and Medicine (NASEM) study (2018) concluded that long-term cannabis smoking is substantially associated with increased respiratory symptoms (i.e., cough, phlegm, and wheeze) and more frequent chronic bronchitis episodes than experienced by non-smokers.
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> By contrast, recent outbreaks of respiratory illnesses associated with consumption of mostly unregulated Delta-9-tetrahydrocannabinol (THC)-containing vaping products have so far resulted in 2807 hospitalizations and 68 deaths in the United States, with additional cases being investigated in Canada (Centers for Disease Control and Prevention (CDC), 2020, Government of Canada, 2020).
> E-cigarette vapor contains many of the known harmful toxicants found in traditional cigarette smoke, such as formaldehyde, cadmium, and lead, though usually at a reduced percentage.[25]
From a quick search: https://onlinelibrary.wiley.com/doi/10.1002/ijc.34643
It's like the fearmongering around MDMA, which claims that there will be delayed harmful effects from meddling with your brain chemistry, but hundreds of millions of users and decades later where is the widespread harm? Arguably it proves that it's one of the safest drugs on earth.
Of course controlled studies are rigorous, but widespread use must also lead to widespread harm if it exists. There may be hidden harm because it's a small effect on a large population or only harms a small population, but that just means it's relatively safe.
