Here are several peer reviewed sources which support using vape cartridges and products free of thinning agents like propylene glycol. Also understand while black market products could be cheaper, there is a VERY high degree of pesticide contamination and potential carcinogenic thinning agents used in unverified products.
The study below found a relationship between PEG in the air and asthma, rhinitis and eczema–>
Take away point –> Only use pure cannabis oil with no thinning agents:
Sources of Propylene Glycol and Glycol Ethers in Air at Home
The study below found that heating propylene glycol to temperatures achieved in vape pens or e-juice can produce dangerous carcinogens–>
The study below found that under stress conditions polyethlyne glycol can form formaldehyde, a carcinogen–>
Formation of formaldehyde in polyethyleneglycol and in poloxamer under stress conditions
What about concentrates? What should you buy tested products?
The study below found 80% of products tested contaminated with residual solvents or pesticides!