Review of human studies on dextromethorphan's psychedelic-like effects and doses

The question

What do human studies actually show about the psychedelic-like effects of dextromethorphan (DXM), a common over-the-counter cough medicine, and how do those effects change with dose?

What they did

Researchers searched three medical databases up to 8 August 2025 for human studies in which DXM was given and its mind-altering effects were measured. They followed a standard review method (PRISMA), registered the plan in advance, and had two reviewers independently screen studies and rate their quality. Because the studies were too different to combine statistically, results were described narratively.

What they found

From 297 records, eight studies covering four unique samples were included, with 104 people in total: an ascending dose-sequence study (n = 12), two crossover studies (n = 20 and n = 32), and a single-dose study (n = 40). Doses ranged from 100 to 960 mg. Psychedelic-type effects were reported starting at 100 mg, while side effects such as nausea, vomiting, impaired movement and slowed thinking became more prominent above 200 mg. Hallucinatory and mystical-type experiences were more intense at 300 and 400 mg. Risk of bias was generally rated as having some concerns or as high, and certainty of evidence was low for most primary outcomes.

The fine print

Only four unique groups of participants, totalling 104 people, underpin the whole review, and the study designs, doses and outcome measures varied widely. Most included studies had quality problems, and none appear to have tested DXM as a treatment for a psychiatric condition, so nothing here shows clinical benefit. The authors state the evidence is too limited to establish a true dose-response relationship. This summary is based on the abstract only.

What it means

Human data on dextromethorphan as a psychedelic-like agent are sparse and of low quality: effects appear at lower doses and intensify at higher ones, but side effects also rise, and no therapeutic benefit has been demonstrated.

Evidence grade: Low. A systematic review of only eight reports from four small samples, most with some or high risk of bias, and the authors themselves rated certainty as low for the main outcomes.

This summary is based on the study’s published abstract.