Smoked vs. Vaporized Cannabis: Equal THC Does Not Mean Equal Exposure

WHY ROUTE MATTERS

A milligram amount is not an absorbed dose.

A cannabis dose written as a number of milligrams can look exact. The number does not establish how much THC reached the bloodstream, how quickly it arrived, or how the person performed afterward.

A controlled 2018 crossover study compared smoked and vaporized cannabis containing the same nominal THC doses in 17 adults who used cannabis infrequently. Vaporized cannabis generally produced stronger measured effects and higher blood THC concentrations than the equal-dose smoked condition. The study also found that blood THC and heart rate returned toward baseline before all subjective, cognitive, and psychomotor effects had ended.

That combination matters in forensic interpretation. Route, delivery efficiency, timing, user experience, and the selected performance measure cannot be replaced by the package dose or a single blood number.

STUDY DESIGN

Six controlled sessions compared route and dose.

The investigators enrolled 17 healthy adults, nine men and eight women, with a mean age of 27.3 years. Participants reported prior cannabis experience but no use during the preceding month. The reported mean time since last use was 398 days, with wide variation.

Each participant completed six outpatient sessions separated by at least one week. The conditions involved smoked and vaporized cannabis containing 0, 10, or 25 mg THC. The inhalation-method order was counterbalanced, and dose order within each method was randomized. Participants inhaled the assigned material during a ten-minute period. The vaporized material was heated with one specified device and collected in a balloon for inhalation.

The researchers measured subjective drug effects, cognitive and psychomotor performance, heart rate, blood pressure, and blood THC. This was a controlled laboratory study, not an on-road driving study and not a validation of a legal impairment cutoff.

DELIVERY EFFICIENCY

Vaporization delivered more THC under the tested conditions.

At equal nominal doses, vaporized cannabis produced higher peak blood THC concentrations and generally stronger pharmacodynamic effects than smoked cannabis. At the 25 mg dose, the reported mean peak blood THC concentration was 14.4 ng/mL after vaporization and 10.2 ng/mL after smoking.

The investigators explained that combustion and sidestream smoke can cause THC loss during smoking. In the study’s fixed-dose procedure, the vaporizer therefore appeared to be a more efficient delivery method.

This finding should not be converted into a universal ratio between smoking and vaporization. The study used one plant material, one vaporizer, one temperature, and a small group of infrequent users. Different devices, temperatures, concentrates, THC-to-CBD ratios, puff patterns, and user behavior may change delivery.

For the general difference between administered dose and measured concentration, see Drug Absorption in Toxicology and Pharmacokinetics in Toxicology.

DOSE AND EFFECT

The 25 mg conditions produced more pronounced changes.

The 10 mg conditions produced recognizable drug effects and modest cognitive impairment. The 25 mg conditions produced more pronounced subjective effects, cognitive and psychomotor impairment, cardiovascular changes, and adverse effects.

Vaporization generally produced the greater changes at an equal nominal dose. This does not prove that every person who vaporizes cannabis will be more impaired than every person who smokes it. It shows that administration method affected delivery and group-level outcomes under the tested protocol.

It also demonstrates why an opinion should identify what the reported dose means. Milligrams placed into a smoking device, milligrams in plant material, milligrams inhaled, and milligrams absorbed are different quantities. A product label or investigator’s assigned dose is not a direct measurement of the absorbed dose in an individual.

CONCENTRATION AND EFFECT

Blood THC declined before every measured effect ended.

Blood THC concentrations and heart rate peaked within 30 minutes after administration and returned to baseline within approximately three to four hours. Several subjective effects and observed cognitive or psychomotor impairments persisted for as long as six hours on average.

The study reported that blood THC was only moderately correlated with subjective effects and was weakly correlated, or not correlated, with cognitive and psychomotor performance. In some instances, effects persisted after blood THC fell below the analytical limit of quantification.

This does not make blood testing useless. Blood analysis can identify compounds, distinguish parent drug from metabolites, and establish concentrations at a documented collection time. It does mean that a blood concentration and a performance conclusion are not interchangeable.

See Whole Blood and Plasma in Toxicology and Cannabis Metabolites in Toxicology for the specimen and analyte distinctions that belong in the analysis.

CASE TIMELINE

Reconstruct events from the record, not from one number.

The forensic timeline should begin with the reported start and end of use, not just the blood-draw time. For inhaled cannabis, concentrations can rise and fall quickly. Performance measures may follow a different time course.

A case review should separate the time cannabis use began and ended; whether the material was smoked or vaporized; the device, product, composition, and reported dose; the time of driving or other conduct; the times of observations and field tests; the time and matrix of each specimen collection; the parent THC and metabolite results; and the analytical reporting limits and uncertainty.

Working backward from a later concentration without accounting for rapid distribution, route-specific delivery, and individual variation can create false precision. For related limitations, see Measurement Uncertainty in Toxicology and Detection Windows in Toxicology.

STUDY LIMITS

Infrequent users are not a model for every person.

The participants were healthy adults who had not used cannabis in the previous 30 days. On average, their last reported use was roughly one year earlier. The results may therefore be especially relevant to acute effects in infrequent users, but they should not automatically be applied to frequent or daily users.

Repeated exposure can be associated with tolerance to some effects, while residual cannabinoids can remain detectable in some frequent users. Neither proposition establishes an individual’s performance. It simply means that user history is a material study-comparison variable.

The researchers also identified the small sample, limited dose range, one high-THC/low-CBD material, and one vaporizer configuration as limitations. A reliable comparison should state those boundaries rather than treating the study as a universal cannabis model.

What this study does not establish

• A per se blood THC concentration for impairment.
• A universal duration of impairment.
• A formula for converting vaporized dose to smoked dose.
• The amount of THC absorbed by a particular person from an unknown device.
• That a person was impaired merely because THC was detected.
• That a person was unimpaired merely because a later blood result was low.
• On-road driving performance at the tested doses.
• How frequent users, patients, or people using different products would respond.

CASE-SPECIFIC REVIEW

Records needed to compare a case with the study.

1. Product and deviceObtain packaging, batch information, cannabinoid composition, photographs, device settings, condition, and instructions.
2. Use historyDocument the reported dose, puff pattern, start and end times, and the person’s prior cannabis experience.
3. PerformanceReview driving video, body-camera video, witness accounts, and contemporaneous observations.
4. TimelineIdentify exact times for driving, contact, testing, arrest, and every specimen collection.
5. Laboratory recordReview the method, calibration, controls, chromatograms, reporting limits, uncertainty, parent THC, 11-hydroxy-THC, and carboxy-THC.
6. AlternativesEvaluate alcohol, medications, other drugs, sleep, medical conditions, anxiety, injury, and competing explanations.

The study becomes useful when its design and limits are compared with the actual case facts. It is not a substitute for those facts.

BOTTOM LINE

Nominal dose, blood concentration, and performance are different evidence.

In this small controlled crossover study of infrequent cannabis users, vaporizing an equal nominal THC dose produced higher blood THC and generally stronger effects than smoking. Blood THC declined toward baseline before all measured subjective, cognitive, and psychomotor effects had ended.

The proper forensic lesson is not that vaporization always produces a fixed additional effect. It is that nominal dose, absorbed dose, blood concentration, and measured performance are different evidentiary variables. Route, device, timing, user history, analytical method, and actual behavior must be evaluated together.

PRIMARY SOURCE

Controlled crossover research.

• Spindle TR, Cone EJ, Schlienz NJ, Mitchell JM, Bigelow GE, Flegel R, Hayes E, Vandrey R. Acute Effects of Smoked and Vaporized Cannabis in Healthy Adults Who Infrequently Use Cannabis: A Crossover Trial. JAMA Network Open. 2018;1(7):e184841. Journal record. PubMed Central. DOI.

This guide paraphrases the published research. The source PDF, publisher layout, tables, and figures are not reproduced.