Cheese, Beer, and Serotonin: Making Sense of MAO Inhibitors

two triangles of cheese next to a glass of beer

The Bottom Line

MAO inhibitors are commonly used for the treatment of Parkinson’s disease and depression. Serious medical conditions can occur if MAO inhibitors are used in higher doses or taken in overdose. In addition, people who take MAO inhibitors should avoid eating certain foods, to reduce their risk of unwanted side effects.

Man using his glasses to read the label on a medicine bottle

The Full Story

Monoamine oxidase (or “MAO”) is an enzyme found in the human body. The MAO enzyme converts chemicals including dopamine, serotonin, and adrenaline into ammonia, hydrogen peroxide, and other products. There are two types of MAO found in the human body. MAO type A (or MAO-A) is found in the stomach and intestines, while most MAO type B (MAO-B) is located in other organs including the brain. 

Since depression is believed to be caused by low levels of “happy hormones” including serotonin, drugs that block or inhibit MAO have been used as antidepressants. MAOI inhibitors keep the “happy hormones” from breaking down. This allows serotonin and other hormones to remain in the brain for longer, and helps to reduce symptoms of depression. These drugs are called “MAO inhibitors” and include phenelzine (Nardil®), tranylcypromine (Parnate®), and isocarboxazid (Marplan®). Because MAO is involved in the metabolism of multiple compounds in the human body and brain, MAO inhibitors have also been used to treat a variety of conditions including anxiety, dementia, and Parkinson’s disease. Since MAO inhibitors cause increases in serotonin and other natural chemicals, they can interact with other antidepressants or drugs that act in a similar way. Serotonin syndrome is a serious medical condition that is caused by the presence of excess serotonin in the human body. Serotonin syndrome can occur when an individual takes multiple medications or high doses of drugs that affect serotonin release or metabolism. Patients who develop serotonin syndrome often require specialized care or hospitalization. Because MAO inhibitors affect serotonin metabolism, people who take MAO inhibitors are at risk for developing serotonin syndrome.

One of the other chemicals targeted and metabolized by MAO inhibitors is called tyramine. In the human body, the presence of excess tyramine causes high blood pressure along with other unpleasant symptoms such as nausea, skin flushing, and headache. This condition is often described as a “tyramine reaction”. Tyramine is present in the human digestive system and is normally metabolized there by MAO-A. The use of MAO inhibitor medications causes high levels of tyramine to build up in the body and can result in tyramine reactions. People who take higher doses of MAO inhibitors, as well as those who overdose on these medications, are at higher risk for developing tyramine reactions. Since tyramine is naturally present in some foods including aged cheeses and meats, draft beer, and sauerkraut, people who take standard prescribed doses of MAO inhibitors may develop tyramine reactions if they eat these foods. Because of this, individuals who take MAO inhibitors are often advised to follow a special low-tyramine diet.

Since tyramine is largely metabolized by MAO-A, the use of MAO-B inhibitors may reduce the risk of developing tyramine reactions. Newer MAO inhibitor drugs, including selegiline (Eldepryl®) and rasagiline (Azilect®), target MAO-B and are called “selective” MAO inhibitors. Selegiline is currently approved by the United States Food and Drug Administration as a treatment for adults with Parkinson’s disease. When used in low doses, selegiline is not associated with the development of tyramine reactions in most patients. However, when high doses of selegiline are taken or when the drug is taken in overdose, tyramine reactions can occur. Patients who experience tyramine reactions may require hospitalization, and the condition can be life-threatening in some cases. There is no antidote available for MAO inhibitor overdose or tyramine reactions, but there are medications available that can be used to reduce the unwanted and unpleasant signs and symptoms caused by these conditions.

Kelly Johnson-Arbor, MD
Medical Toxicologist

Poisoned?

Call 1-800-222-1222 or

HELP ME online

Prevention Tips

  • Only take MAO inhibitors as always prescribed and always keep them out of reach of children.
  • Following a low-tyramine diet may reduce the risk of developing a tyramine reaction.
  • Talk with your doctor or pharmacist before taking any new prescriptions or over-the-counter medications in combination with MAO inhibitors to reduce your risk of developing serious side effects, including serotonin syndrome.

This Really Happened

A 27-year-old man was hospitalized for depression and treated with phenelzine (Nardil®). While out of the hospital on a pass, he drank a single glass of Upper Canada Lager draft beer. Within a half hour of drinking the beer, he developed a sudden onset severe headache, chest pain, nausea, and dizziness. He returned to the hospital and was found to have a blood pressure of 220/120 mmHg (normal is about 120/80 mmHg). He was treated with antihypertensive medications, and his blood pressure returned to normal values. His illness was attributed to elevated levels of tyramine that are present in draft (tap) beer. The high tyramine levels in draft beer are believed to occur due to bacterial contamination of the lines leading from the keg to the tap.


For More Information

If you have a question about poisoning from MAO inhibitors including selegiline, phenelzine, or tranylcypromine, get help online with webPOISONCONTROL or call 1-800-222-1222. Both options are free for the public, and available 24 hours a day.


References

Linden CH, Rumack BH, Strehlke C. Monoamine oxidase inhibitor overdose. Ann Emerg Med. 1984 Dec;13(12):1137-44. 

Magyar K. The pharmacology of selegiline. Int Rev Neurobiol. 2011;100:65-84. 

Ostadkarampour M, Putnins EE. Monoamine Oxidase Inhibitors: A Review of Their Anti-Inflammatory Therapeutic Potential and Mechanisms of Action. Front Pharmacol. 2021 Apr 30;12:676239. 

Rafehi M, Faltraco F, Matthaei J, Prukop T, Jensen O, Grytzmann A, Blome FG, Berger RG, Krings U, Vormfelde SV, Tzvetkov MV, Brockmöller J. Highly Variable Pharmacokinetics of Tyramine in Humans and Polymorphisms in OCT1, CYP2D6, and MAO-A. Front Pharmacol. 2019 Oct 30;10:1297.

Shulman KI, Tailor SA, Walker SE, Gardner DM. Tap (draft) beer and monoamine oxidase inhibitor dietary restrictions. Can J Psychiatry. 1997 Apr;42(3):310-2. 

Wimbiscus M, Kostenko O, Malone D. MAO inhibitors: risks, benefits, and lore. Cleve Clin J Med. 2010 Dec;77(12):859-82.

Youdim MB, Edmondson D, Tipton KF. The therapeutic potential of monoamine oxidase inhibitors. Nat Rev Neurosci. 2006 Apr;7(4):295-309

Poisoned?

Call 1-800-222-1222 or

HELP ME online

Prevention Tips

  • Only take MAO inhibitors as always prescribed and always keep them out of reach of children.
  • Following a low-tyramine diet may reduce the risk of developing a tyramine reaction.
  • Talk with your doctor or pharmacist before taking any new prescriptions or over-the-counter medications in combination with MAO inhibitors to reduce your risk of developing serious side effects, including serotonin syndrome.

This Really Happened

A 27-year-old man was hospitalized for depression and treated with phenelzine (Nardil®). While out of the hospital on a pass, he drank a single glass of Upper Canada Lager draft beer. Within a half hour of drinking the beer, he developed a sudden onset severe headache, chest pain, nausea, and dizziness. He returned to the hospital and was found to have a blood pressure of 220/120 mmHg (normal is about 120/80 mmHg). He was treated with antihypertensive medications, and his blood pressure returned to normal values. His illness was attributed to elevated levels of tyramine that are present in draft (tap) beer. The high tyramine levels in draft beer are believed to occur due to bacterial contamination of the lines leading from the keg to the tap.