We also performed gas chromatography–mass spectrometry (GC-MS) analysis on all tested e-liquids. Subsequent nonmetric multidimensional scaling (NMDS) analysis revealed that e-liquids are an extremely heterogeneous group.
AKA: Lots of variation in most e-liquids.
Furthermore, these data indicated that (i) the more chemicals contained in an e-liquid, the more toxic it was likely to be and (ii) the presence of vanillin was associated with higher toxicity values.
Probably the most relevant takeaway. The fewer solvents and other chemicals, the lower the toxicity. Strangely, vanillin, the chemical responsible for the flavor of vanilla, was also associated with higher toxicity.
Now obviously this study was focused on e-cigarettes, but the results may still be applicable to cannabis vaping. They also set up a website devoted to studying e-liquids: