Cannabis consumers have been debating for decades whether smoking from a bong is more harmful than using smoke in a joint. A bong is a device that draws smoke through water to inhale. Water filtration has been a part of conventional wisdom for decades. It is believed to make consumption safer and cleaner.
According to a study conducted by the University of Wisconsin-Madison, and authors in Thailand, “bong-water doesn’t seem to be able filter smoke compounds significantly.”
For the study, researchers analyzed the chemical makeup of smoke from three popular cannabis strains—Bubble Gum, Silver Haze and Hang Over OG—when consumed through both joints and bongs. They looked at the differences between the smoke produced by three popular cannabis strains, Silver Haze, Bubble Gum and Hang Over OG.
Both methods produced results that were almost identical. Bong water failed to completely remove the compounds detected within the measurement range. There were no compounds found in only joint smoke or bong smoking, suggesting that the water was not able to capture all components.
Both the joint and bong smoking showed similar compositions. “No compounds between 5 and 350 g/mol have been completely filtered out by bongwater.”
The researchers note in the paper, published as a pre-print on bioRxiv, that their methods couldn’t capture larger particles, aerosols or metals—in other words, things that water might catch. The findings do not support the notion that bongs reduce exposure to hazardous chemicals.
This study, although it does not reveal the efficacy of filtration in the bong, sheds some light on the composition of smoke from cannabis,” the researchers concluded.
This study shows that compounds found in high concentrations are also promising. They note that the prevalence of β-cis-Caryophyllene, which was consistently present in the highest quantities, suggests “possible physiological importance despite limited research compared to THC and CBD.” The compound is also said to have anti-inflammatory activity, as well as antioxidant, anticarcinogenic, and local anesthetic properties.
According to researchers, one of the major obstacles for cannabis research is the lack standardized instruments that can measure the actual content of smoke. In contrast, tobacco research relies upon decades-old standardized methodologies that allow for comparison of cigarettes from different brands and countries.
The authors wrote: “Establishing standards for analytical methods could help to improve the accuracy of assessments on cannabis quality, therapeutic potential and health risks. It would also allow comparisons between strains and cultivation techniques, as well global research efforts.
Authors warn of methodological restrictions, such as the sample size and loss in smoke during collection. The Agilent GC/MS had limitations in terms of its ability to detect larger particles, metal ions and aerosols. This limited the conclusions that could be made about bong filtration. They wrote that “the findings demonstrate that cannabis smoke is a mixture of harmful compounds and those which may be beneficial.”
The researchers stress that more standardized methods—such as better ways of measuring larger aerosols and analyzing the bong water itself—will be needed to draw firmer conclusions.
This study was not peer-reviewed. A bioRxiv update states that the authors withdrew their paper recently “because it may have been a bureaucracy problem due to the place this research has taken place”.
Bong water became a topic of policy interest in the U.S. when the Minnesota Supreme Court ruled in 2009 that it could be legally considered a drug, in part due to a state patrol officer testifying that marijuana users keep bong water “for future use…either drinking it or shooting it in the veins.” This year, the state’s law was changed by the legislators and governor who passed a new law which ended the possibility of spending decades behind bars for drug residue.
Minnesota’s law was brought to national attention in 2024, when a Fargo-based woman who had been caught using bong water faced a possible 30-year sentence. Minnesota ACLU was called in to defend her due to the severity of the charges.