I question how safe it is to vape O-acetate (which is also an ester?)
it's incredibly smooth when vaping but it has this really odd delayed harshness/cough that comes on 10-20+ min later after vaping it. It makes me speculate that first stage metabolization actually occurs in the lungs? Why else would it take something 10 minutes to make you cough?
Some of the brands going around like Binoid actually cause even additional lung pain/wheezing/etc. It really feels unhealthy. It might be the MCT oil in that specific brand, I'm not sure.
Yeah unfortunately it's difficult to assess the level of risk due to the lack of info.
Could be nothing more than some minor irritation, or something more serious...
So it seems like some brands cause much more discomfort than others. As you said, it could be (partly) caused by the MCT oil or some other compound/impurity.
Could you tell a bit more about those "delayed" side-effects? Is it like the typical cough you get cannabis products? Or do you experience breathing difficulties or something like that as well? (This doesn't really happen with cannabis as THC acts as a bronchodilator).
If I had to speculate, I'd say it could be cause by one of these things:
1) An intrinsic property of THC-O-acetate, such as the very high lipophilicity. It could very well take 10-30min or more for the irritation/damage to become really noticeable.
In this case the mechanism may be similar to the one from vitamin E acetate, but less severe. If I'm not mistaken, e-liquids also contained much more vit E acetate than the desired cannabinoid (THC, THC-O-Ac, etc...), right?
Or it could be a completely different mechanism, the O-acetate derivative could be having an unknown effect on lung cells (interacting with certain proteins/receptors, etc.).
2) Impurities/contaminants in the e-liquid, or by-products formed during the heating process.
Regarding the metabolism hypothesis. The quickest and most likely transformation would be the hydrolysis of the ester, producing acetic acid and THC. Hydrolase enzymes could (potentially) catalyse this reaction (some of them are present in the lungs).
However, I doubt this is the main cause of the problem, the amount of acetic acid produced would likely be too small to cause significant problems. Otherwise heroin smokers would experience a much more severe version of this, not only is acetic acid produced along with 6-MAM, there's often some acetic acid within the product as well (it's an impurity from the manufacturing process).