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Compound Monograph

Harman

Harman is a beta-carboline alkaloid found in many plants and also formed in cooked foods and tobacco smoke.

Work in progress

Classification

Harman is a beta-carboline alkaloid, part of the alkaloids class. Nitrogen-containing, often bitter and physiologically potent compounds — the group behind many of the strongest plant medicines and poisons.

Alkaloids Indole Alkaloids

Where Does It Come From? (5)

Harman is a naturally occurring beta-carboline alkaloid, found in Common reed, Passionflower, Tobacco smoke and various cooked foods and 2 other sources. It is flagged as moderately toxic.

Cat's Claw Uncaria tomentosa Common reed Passionflower Passiflora incarnata Tobacco smoke and various cooked foods Tribulus Tribulus terrestris

Research & Evidence

Harman (harmane) is a beta-carboline alkaloid that is widely distributed in the plant kingdom and is also formed in small amounts during the cooking of meat and in tobacco smoke and coffee. Like related beta-carbolines it can inhibit monoamine oxidase and interact with several neurotransmitter systems. It occurs at low levels in human tissues, and research interest has focused on its possible relationships to tremor and other neurological endpoints rather than on any deliberate psychoactive use.

Monoamine oxidase (MAO) inhibition

Like other β-carbolines, harman is a MAO-A-selective inhibitor, and a potent one — reported as a reversible, competitive inhibitor with sub-micromolar potency (IC50 in the region of 0.06 µM in one recombinant-enzyme assay) and only weak activity against MAO-B 1Reference 1Saro et al. · 2025Monoamine oxidase inhibitors present in tobacco modulate dopamine balance via the dopamine transporterView study →. Because harman forms during cooking and is present in tobacco smoke and coffee, this activity is usually discussed in the context of low-level dietary and environmental MAO inhibition rather than deliberate use. See the natural MAO inhibitors guide for how the β-carbolines compare.

Toxicity & Safety

As a monoamine oxidase inhibiting beta-carboline, harman shares the interaction cautions of this group. It is mostly encountered as a trace dietary and environmental compound rather than something taken on purpose, and its effects at such low exposures are not well characterised.

References

  1. Saro, G., Johne, S., Latino, D. A. R. S., Moine, F., van der Toorn, M., Mathis, C., & Veljkovic, E. (2025). Monoamine oxidase inhibitors present in tobacco modulate dopamine balance via the dopamine transporter. ACS Chemical Neuroscience, 16(6), 1117-1131. https://pubmed.ncbi.nlm.nih.gov/40033845/