Requested Cannabis Abstinence Did Not Mean Every Imaging Screen Was Negative

Participants were asked to refrain from cannabis for ninety-six hours, but some high-risk participants had THC-positive urine screens. The screening result and requested interval are different pieces of exposure information.

The paper documented the distinction

The imaging protocol specified abstinence from cannabis, alcohol, nicotine and other recreational drugs for defined periods. Its baseline table nevertheless included THC-positive urine results in both high-risk treatment groups, as well as missing screens. Healthy comparators were selected for minimal drug use and had negative screens.

A positive urine result cannot precisely date use

Residual urinary cannabinoid detection can outlast recent consumption. The screen therefore does not by itself prove that someone violated the ninety-six-hour request or was acutely impaired during scanning. It also does not independently verify that the requested interval was observed. More detailed exposure evidence would be needed to resolve that timing question.

Keep the comparison’s population visible

Drug-use history differed between the clinical-risk and healthy groups. Randomization between CBD and placebo is a different protection from matching either group to minimally exposed healthy participants. The acute BOLD findings and null task-performance comparison should be interpreted within that context, without attributing a specific participant’s activation to an unverified timing-of-use claim.

Related analysis: brain activation and the null task-performance result.

Research cited

Bhattacharyya and colleagues (2018). Effect of Cannabidiol on Medial Temporal, Midbrain, and Striatal Dysfunction in People at Clinical High Risk of Psychosis. DOI: 10.1001/jamapsychiatry.2018.2309.