Scientists Discover a Key Difference Between Smoking Weed and Vaping It

The vape debate gets even hazier.

When Cool Teens started vaping weed at increasingly higher rates, they inadvertently exposed a scientific grey area: Is there actually a difference between smoking weed and vaping it? A study published Friday in JAMA Network Open has an answer, though it may not be that comforting to vape enthusiasts.

This small study, overseen by Johns Hopkins School of Medicine’s Ryan Vandrey, Ph.D., an associate professor of psychiatry and behavioral sciences, is really all about the delivery of THC — the psychoactive compound in weed. The various ways THC gets into the body produces effects on radically different timescales (as anyone who’s experienced edibles can attest).

Vaping, the authors demonstrate with results from 17 participants, turned out to be a more efficient way of delivering THC to the blood, but it also changed the study participants’ experience of the THC dose. The significant differences they found weren’t exactly positive: The vapers noted more intense feelings of paranoia and had drier mouths and eyes than the smokers did.

Vaping generates less sidestream smoke, which could explain why these researchers found it was a more efficient method of THC delivery.


This evidence that vapers experience the effects of THC differently contradicts previous work that showed no significant differences between the two methods. The authors of the new study argue that this is due to their meticulous experimental design: They kept their THC dosage constant by painstakingly calculating the THC percentage in each batch of federally-sponsored weed. Each participant got either zero (a control), ten, or 25 milligrams of THC and then reported their experiences of each dose in each condition over six different trials (everyone got a chance to vape and a chance to smoke).

For the smokers, blood THC levels peaked around 3.8 nanograms per milliliter of blood when they received 10 milligrams of THC. The vapers, on the other hand, ended up with much more THC in their bodies, peaking at 7.5 nanograms per milliliter of blood. This pattern was repeated when the participants got higher doses: vapers had 14.4 nanograms of THC per milliliter of blood, and smokers only had 10.2.

Taken together, the results provide evidence that vaping is at least a more efficient method of THC delivery than smoking, says University of Wollongong psychologist Nadia Solowij, Ph.D., in her accompanying commentary. Vaping, she says, avoids combustion, which tends to burn off THC (and produce harmful byproducts), and also produce far less “sidestream smoke” — the kind that doesn’t end up in a person’s lungs.

“Vaporization has been suggested as a safer intrapulmonary delivery system than smoking, since by heating rather than combusting plant matter it avoids the formation of pyrolytic toxic compounds, including carbon monoxide and carcinogens,” Solowij writes.

The team concludes that vaping marijuana may reduce exposure to some contaminants that come from combustion, which is basically the same argument that’s always being made in favor of e-cigarettes. Whether this means that vaping is actually safer, however, is still out for debate.

“There is, however, little robust evidence from clinical trials or epidemiological studies to support vaporization being a safer option,” Solowij continues.

While this paper suggests that vaping is a better way to deliver THC to the blood, the larger takeaway is that it’s probably not worth it, considering we’re not sure how safe it is and it seems to be accompanied by unpleasant side effects. Maybe not great news for teens, but probably good news for Scott Gottlieb, who may be able to sidestep a whole new front in his war on vaping.

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