What are monoamine oxidase (MAO) inhibitors? How do they interact with other drugs?

Quick Answer
A group of antidepressant drugs.
Expert Answers
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Effect: Dangerous Interaction

Because it contains the stimulant ephedrine, combining the herb ephedra with monoamine oxidase (MAO) inhibitors can rapidly produce a severe, dangerous interaction and should be avoided. In the United States, it is illegal to sell products containing ephedra.

Scotch Broom

Effect: Dangerous Interaction

The herb scotch broom contains high levels of tyramine, so it should not be taken with MAO inhibitors.

Green Tea

Effect: Probable Dangerous Interaction

Because it contains caffeine, green tea should not be combined with MAO inhibitors.


Effect: Possible Dangerous Interaction

According to one report, the combination of ginseng and the MAO inhibitor phenelzine caused worrisome symptoms. While this may have been caused by caffeine contamination of the ginseng, experts recommend avoiding ginseng-MAO inhibitor combinations.

St. John’s Wort

Effect: Possible Dangerous Interaction

Current thinking suggests that St. John’s wort functions somewhat similarly to SSRI (selective serotonin-reuptake inhibitor) antidepressants. Because SSRIs should not be combined with MAO inhibitors, St. John’s wort probably should not be combined with them either.

5-hydroxytryptophan (5-HTP), S-adenosylmethionine (SAMe)

Effect: Possible Dangerous Interactions

Based on one case report and on current thinking about how they work, SAMe and 5-HTP should not be combined with MAO inhibitors.


Brinker, F. “Interactions of Pharmaceutical and Botanical Medicines.” Journal of Naturopathic Medicine 7 (1997): 14.

Iruela, L. M., et al. “Toxic Interaction of S-adenosylmethionine and Clomipramine.” American Journal of Psychiatry 150 (1993): 522.

Jones, B. D., and A. M. Runikis. “Interaction of Ginseng with Phenelzine.” Journal of Clinical Psychopharmacology 7 (1987): 201-202.