Intravenous methamphetamine produced mild psychotic-like symptoms in a small controlled experiment, but did not significantly change how much evidence participants gathered before a decision on a beads task. Symptoms and information gathering were separate measured outcomes, and their results should remain separate.
Ermakova and colleagues analyzed 17 healthy volunteers in a blinded crossover experiment. The three visits involved saline and placebo, intravenous methamphetamine at 0.3 mg/kg with placebo, or methamphetamine after 400 mg oral amisulpride. One enrolled participant was excluded after a suspected administration error.
Participants viewed sequences of beads and decided which of two jars was their source. They could request additional beads before deciding. The number requested, called draws to decision, measured evidence gathering in this particular probabilistic task. Easier and harder bead ratios tested the effect of task difficulty.
Drug condition did not significantly affect draws to decision. Participants requested more evidence in the harder condition, and information-gathering patterns were stable across visits. Methamphetamine nevertheless elicited mild psychotic-like symptoms on the study’s symptom assessment. The experiment therefore does not support treating a symptom change as proof of altered evidence gathering on this task.
A reported relationship between baseline information gathering and symptoms under the methamphetamine-plus-amisulpride condition was exploratory and should retain that treatment context. It does not create a screening test for future psychosis or an individual prediction rule.
This was acute human drug-administration research, not an animal study, a review or a forensic case report. The exposure was a known intravenous dose; it cannot be translated directly into a blood or urine impairment cutoff. Nor was the task a test of driving, witness accuracy, legal competence or criminal responsibility.
The sample was small and healthy. A brief task several hours after a single dose differs from repeated consumption, sleep loss and a real dispute involving emotional or social information. A nonsignificant group result is not proof that every participant’s reasoning was unaffected in every setting.
A forensic account should specify the behavior at issue and ask whether the experiment measured something comparable. Evidence gathering, psychotic symptoms, subjective confidence and vehicle control are different constructs. This study is useful precisely because those outcomes did not move together.
For another example of task-specific inference, see our analysis of simulated driving after d-methamphetamine. Neither study supports a universal statement about all decisions made after exposure.
Read the original investigation: doi:10.1371/journal.pone.0102683.