A single dose of cannabidiol (CBD) does not improve selective attention in people with schizophrenia, and higher doses may worsen performance. In a study of 28 patients, those given 600 mg of CBD performed worse on the Stroop Color Word Test than those given 300 mg or placebo, while all groups showed some improvement from practice. No differences were found in electrodermal responses to sounds. The authors suggest that chronic CBD administration might still be beneficial, but acute treatment appears ineffective for cognitive symptoms.
Ayahuasca, a hallucinogenic brew used by Amazonian indigenous groups, contains β-carbolines that inhibit monoamine oxidase and dimethyltryptamine, a serotonin receptor agonist. Acute administration causes moderate cardiovascular effects in healthy volunteers, but long-term effects are unknown. In rats, ayahuasca (2-4 mL/kg) flattened and stretched vascular smooth muscle cells and altered collagen and elastic fiber arrangement. Chronic high-dose treatment increased media thickness and the ratio of media thickness to lumen diameter in the aorta. More research on cardiovascular function in long-term ayahuasca consumers is needed.