A person reporting less stimulation has not necessarily experienced less cardiovascular stress. Subjective ratings, pulse and blood pressure answer different questions, even when they are collected during the same drug challenge.
What did the historical trial find?
Verrico and colleagues’ 2016 double-blind laboratory study randomized 60 non-treatment-seeking adults with methamphetamine use disorder; complete data were available for 59. Oral perindopril conditions were placebo, 4, 8 or 16 mg/day. After 5–7 days, participants received 15- and 30-mg intravenous methamphetamine challenges on alternate days.
The 8-mg perindopril group had lower peak anxious and stimulated ratings than placebo after correction for multiple comparisons (p=0.0009 and p=0.0070). A greater perindopril dose did not produce a progressively greater effect. Posttreatment cardiovascular treatment comparisons were nonsignificant; methamphetamine still increased the cardiovascular measures. Treatment-by-methamphetamine interactions were nonsignificant across the subjective ratings and cardiovascular measures.
A treatment main effect is not a drug-specific interaction
The study excluded important medical and psychiatric comorbidities and used a brief inpatient protocol. It did not establish outpatient abstinence or prevention of cardiovascular events.
A main effect of treatment describes a difference across treatment groups under the fitted model. An interaction asks whether the response to methamphetamine changes with treatment in the modeled comparison. Those propositions should not be treated as interchangeable merely because the experiment included both drugs.
The distinction is particularly useful when evaluating a claim that perindopril specifically blocked a methamphetamine effect. Such a claim should identify the relevant comparison and acknowledge the interaction result. The lower ratings remain findings; explaining their statistical form prevents them from acquiring a stronger mechanism claim than the analysis supplies.
Why the cardiovascular result must remain visible
It would be inappropriate to infer cardiovascular protection from reduced anxiety or stimulation scores. Demonstrating protection would require a suitable cardiovascular outcome and enough evidence to evaluate that outcome. A symptom rating cannot supply an unmeasured event comparison.
A nonsignificant cardiovascular difference also does not prove that the regimens are equivalent. That conclusion would require a suitable equivalence question, margins and precision. An ordinary null comparison and a successful equivalence test have different meanings.
The appropriate use of this paper is therefore narrow but valuable: it identifies a selected subjective signal within a controlled human experiment while retaining the cardiovascular null findings and the irregular dose pattern. It does not justify taking perindopril to counteract methamphetamine, nor does it predict an individual’s medical safety from how stimulated they feel.
Source
Verrico CD, et al. Subjective and Cardiovascular Effects of Intravenous Methamphetamine during Perindopril Maintenance: A Randomized, Double-Blind, Placebo-Controlled Human Laboratory Study. Int J Neuropsychopharmacol. 2016;19:pyw029. doi:10.1093/ijnp/pyw029. Full text.