PG and PEG in Cannabis Vaping: A Critical Review of Heating Conditions, Cannabinoid Delivery, and Alternatives to Combustion

Propylene glycol (PG) and polyethylene glycol (PEG) cannabis liquidizers should be evaluated as components of noncombustion delivery systems against the methods and formulations they replace. Human studies show that cannabis vaporization can maintain or increase delta-9-tetrahydrocannabinol (THC) delivery while reducing measured combustion exposure. Analytical comparisons also demonstrate fewer pyrolytic compounds and lower modeled risks from selected gas-phase toxicants. Carrier research supplies additional reasons to reject the presumption that glycol free or botanical alternatives are necessarily better: PG has favorable controlled exposure findings and outperformed phytol in a direct animal comparison. Prominent aldehyde claims have also been challenged by work examining aversive heating and exposure realism. The evidence therefore supports a comparative, formulation-specific case for PG and PEG liquidizers rather than categorical rejection based on ingredient names or isolated heating tests. This review examines those arguments, the limits of their application, and competing additives. It distinguishes the broader PG research record from the more limited PEG record. No clinical ranking of every carrier or original product testing is presented.Version 2.0 revises The Science of Safety and corrects related scientific statements in Why Settle: The War on Vapor. This is a company-supported narrative review, not an independently peer-reviewed product evaluation. Kenneth Fry is the founder of Terps USA, which sells liquidizers and has a commercial interest in the subject. Generative AI assisted drafting, source identification, and editorial preparation; it is not an author.