If you’ve ever been a stoner who hit bottom, then you are all too familiar with the temptation of smoking pipe resin. Pipe resin, sometimes called “reclaim” depending on regional use, is that black tar that builds up on a smoking apparatus such as a bong or pipe over the course of dozens or hundreds of hits. (This is not to be confused with the good kind of resin, the sap which you find on really good nugs, or live resin, the hash which is extracted through a process involving freezing whole cannabis plants).

As many of you know, one may end up smoking pipe resin when one is out of weed and unable to promptly find a new hookup. You scrape it out with a paperclip or something and then smoke that nasty-tasting stuff until you forget  your troubles again. And then, god help you, if you don’t get a new hookup, you might smoke the leftover resin-resin.

But one doctor is warning that this is probably not such a hot idea.

“While it’s true that cannabis is generally safe for use in healthy adults, it’s important to exercise common sense,” writes Dr. Jordan Tischler MD on the website The Growth Op.

Like some cannabis extracts, pipe resin or reclaim “can retain a concentration of pesticides, heavy metals, residual solvents, and toxins — none of which are substances you want entering your body. Moreover, let’s not forget reclaim’s main component: tar. Smoking tar, under any circumstances, is harmful to your lungs. Just because the respiratory risks of cannabis use are smaller than those associated with tobacco use, that doesn’t mean smoking a tar-based byproduct of cannabis is safe.”

Tischler is a self-described “Harvard-trained Holistic Care expert,” which sounds a lot like a doctor who didn’t got to Harvard, but the dude has other qualifications. Like, he was cited in Leafly which called him a doctor “who does great work in the field of sex and cannabis.” There’s also his soul patch, which is cooler than it sounds.

Tischler also says that the content of your average reclaime is slightly higher than that of cannabis flower, but that the chemical contents of reclaim are impossible to gauge without sophisticated laboratory equipment” and that “only does this make reclaim dosing imprecise to the point of uselessness, it’s also a rather inefficient – and dirty – way of administering THC.”

So basically it’s like some of the worst hash you can find.

He also recommends refraining from smoking in general, and instead embracing the more lung-healthy method of vaporization, which can’t hurt.