A 10 mg THC Brownie Changed Subjective Effects Without Detectable Task Deficits

In a small crossover trial, a 10 mg THC brownie produced subjective drug effects without significant performance deficits on the tested tasks compared with placebo. Higher doses impaired performance. The 10 mg finding is an endpoint-specific null result, not proof that this dose is safe for every person or activity.

Participants served as their own controls

The study involved 17 healthy adults who used cannabis infrequently. Each completed separate sessions with brownies containing 0, 10, 25 or 50 mg THC, with at least one week between sessions. The randomized, blinded comparison reduced the influence of stable differences between people.

Investigators collected repeated blood samples and assessed subjective effects, cardiovascular responses and cognitive or psychomotor performance. The tasks included divided attention, digit-symbol substitution and paced serial addition. These laboratory outcomes were not a direct driving test.

The dose pattern was not all-or-nothing

The 10 mg dose significantly increased ratings of drug effect and good drug effect relative to placebo. It also increased heart rate. Yet performance on the tested tasks did not significantly differ from placebo at that dose.

The 25 and 50 mg conditions produced performance deficits on multiple measures, with the detailed pattern varying by task and endpoint. Blood pressure did not show a significant overall dose effect. Reporting only “THC impaired cognition” would omit the lower-dose null finding; reporting only that null would omit measurable drug effects and the higher-dose results.

Why the null is not a safety guarantee

Seventeen participants cannot establish equivalence across all users, products and activities. The study selected healthy infrequent users and administered prepared brownies under controlled conditions. Other formulations, food conditions, concurrent drugs and individual susceptibility may change responses.

A subjective high, a blood concentration and a performance score are different observations. None should silently replace another. The delayed effects of oral cannabis also mean that an early observation may not characterize the entire session.

For forensic interpretation, retain the dose, route, sampling time and actual functional evidence. Our article on THC concentration and impairment addresses why a numerical result alone cannot determine a person’s condition at an earlier event.

Primary research

Nicolas J. Schlienz and colleagues. Drug and alcohol dependence (2020). Pharmacodynamic dose effects of oral cannabis ingestion in healthy adults who infrequently use cannabis.