At least four scientific studies have examined vaporizers. Studies have found the release of harmful constituents dramatically reduced or completely eliminated. Substantial reductions were also found for the M1-volatizer. However, a 1996 study including two simple vaporizers still found ten times more tar in the vapor than THC, although this was nevertheless up to a 30% improvement compared to the best alternative smoking method.
The most recent study (2006), performed by researchers at Leiden University, tested a Volcano Vaporizer with preparations of pure THC and found that:
“Our results show that a safe and effective cannabinoid delivery system seems to be available to patients. The final pulmonal uptake of THC is comparable to the smoking of cannabis, while avoiding the respiratory disadvantages of smoking.”
When using plant material (crude flower tops), besides THC, several other cannabinoids as well as a range of other plant components including terpenoids were detected in the plant material. However, using pure THC in the Volcano, no degradation products (delta-8-THC (D8-THC), cannabinol (CBN), or unknown compounds) were detected by HPLC analysis. Also, a substantially larger fraction of the THC was delivered to the vapor by using pure THC.
Analysis of the vapor from the Volcano found that using multiple passes it delivered 36% – 61% of the THC in the sample  – a more recent study using pure cannabinoid preparations achieved a maximum of 54%.  For comparison, studies of cannabis cigarettes smoked via a smoking machine under varying conditions of puff duration and air speed found very similar efficiencies of 34% to 61%. Consequently, users can achieve the desired effect with a similar amount of material as when smoking.
In a 2001 study testing a device called the M1 Volatizer®, the researchers found that “it is possible vaporize medically active THC by heating marijuana to a temperature short of the point of combustion, thereby eliminating or substantially reducing harmful smoke toxins that are normally present in marijuana smoke”. The M1 Volatizer, produced THC at a temperature of 365 degrees Fahrenheit (185 degrees Celsius), while completely eliminating three measured combustion products, benzene, toluene and naphthalene. Carbon monoxide and smoke tars were also reduced, but not quantified.
These positive results are in contrast to MAPS/NORML’s previous studies into vaporizers which found less encouraging results, leading one to the conclusion that the effectiveness of vaporization varies greatly from vaporizer to vaporizer. See Factors affecting vaporizer output for possible causes of variation.
A 1996 MAPS study tested two simple vaporizer models against water pipes and filtered and unfiltered cannabis cigarettes (joints). The smoke produced by each was analyzed for solid particulates (tars) and 3 major cannabinoids. The various smoking methods were then rated based on their cannabinoid-to-tar ratio. The two tested vaporizers performed up to 25% better than unfiltered cannabis cigarettes (second best) in terms of tar delivery. However, both vaporizers produced more than ten times more tars than cannabinoids, which may partly be attributable to the low potency (2.3%) of the NIDA-supplied cannabis used in the study. Surprisingly, the same study found that water pipes (bongs) and filtered cigarettes performed 30% worse than regular, unfiltered joints. The reason was that waterpipes and filters filter out psychoactive THC with the tars, thereby requiring users to smoke more to reach their desired effect. The study did not, however, rule out the possibility that waterpipes could have other benefits, such as filtering out harmful gases such as carbon monoxide.
These studies have not measured the presence of toxic gases, such as ammonia, hydrogen cyanide and carbon monoxide, though previous studies have indicated unquantified decreases in carbon monoxide with vaporization.
Although vaporizers produce cleaner vapors than smoking, they do not completely eliminate respiratory irritation. A puff of strong vaporized cannabis will occasionally cause coughing. This however, could be due to THC itself, which is known to have a strong expectorant effect.
Factors affecting vaporizer extraction and delivery capabilities and the breadth of spectrum of actives deliverable
The wide range of results from tests of different vaporizers suggest that the choice of vaporizer is a major factor in determining extraction and delivery efficiency as well as the amount of harmful byproducts produced, or not produced, as in the case of a superior system. In Cannabis, and many other medicinal plants, the components responsible for the aromatic nature of the plant will often vaporize at a low-end temperature in the range of extraction temperature values for all the bioactive components. In Cannabis, the temperature range across which the actives will vaporize is at least 132 degrees F starting at around 260F where only aromatic compounds of minimal bioactivity will release and going all the way up to 392F with the higher end of this range representing where the cannabinoids of higher bioactivity appear to be released. It is believed that both the total amount of actives delivered as well as the breadth of spectrum delivered per inhalation is critical in determining the value of the delivered dose and, in turn, systems that deliver the highest amount of actives and broadest spectrum of actives per inhalation are believed to be the most effective for medicinal applications.
Proposed factors affecting output include:
- specimen density
- weight, content of water and essential oils
- consistency of material in the filling chamber
- variety and potency of cannabis used
- different preparations such as crude flowertops, hashish, hash oil, etc.
- storage time of the vapor
- proportion of THC exhaled (breathing technique)
Not all those have been scientifically tested. Research using the vaporizer found the delivery efficiency highest at around 226 degrees Celsius, falling to about half efficiency at 150 to 180 degrees depending on material . The purest preparations produced the highest efficiencies, about 54% for pure THC versus 29% for plant material (female flowertops) with 12% THCA content. Besides THC, several other cannabinoids as well as a range of other plant components including terpenoids were detected in the plant material. Using pure THC in the Volcano, no degradation products (delta-8-THC (D8-THC), cannabinol (CBN), or unknown compounds were detected by HPLC analysis.
The longer vapor is stored, the more of the THC is lost as it condenses on the surface of the vaporizer or the balloon. This loss may be negligible over a few minutes but may exceed 50% after 90 minutes.
Interestingly, the Leiden Univsersity study found that as much as 30%–40% of inhaled THC was not absorbed by the lungs and simply exhaled. However, they did not find large individual differences in the amounts exhaled.