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MAO Inhibitors: Effects, Uses & Side Effects
MAO inhibitors are medications that block the enzyme monoamine oxidase, preventing the breakdown of neurotransmitters like serotonin. They are primarily used to treat depression.
Add as Preferred SourceThings worth knowing about "MAO inhibitors"
MAO inhibitors are medications that block the enzyme monoamine oxidase, preventing the breakdown of neurotransmitters like serotonin. They are primarily used to treat depression.
What Are MAO Inhibitors?
MAO inhibitors (monoamine oxidase inhibitors, MAOIs) are a class of medications that block the enzyme monoamine oxidase (MAO). This enzyme is responsible for breaking down certain chemical messengers in the brain, known as monoamines, including serotonin, norepinephrine, and dopamine. By inhibiting MAO, these neurotransmitters remain available in the brain for longer periods, which can elevate mood and improve mental well-being.
Indications – When Are MAO Inhibitors Used?
MAO inhibitors are primarily prescribed for the following conditions:
- Depression, particularly treatment-resistant forms
- Anxiety disorders and panic disorders
- Social phobia
- Post-traumatic stress disorder (PTSD)
- Parkinson's disease (MAO-B inhibitors such as selegiline)
- Atypical depression
Mechanism of Action
The enzyme monoamine oxidase exists in two subtypes: MAO-A and MAO-B. MAO-A primarily breaks down serotonin and norepinephrine, while MAO-B mainly degrades dopamine. MAO inhibitors target one or both of these subtypes:
- Non-selective MAO inhibitors (e.g., phenelzine, tranylcypromine) inhibit both MAO-A and MAO-B.
- Selective MAO-A inhibitors (e.g., moclobemide) reversibly inhibit MAO-A and are referred to as RIMAs (reversible inhibitors of monoamine oxidase A).
- Selective MAO-B inhibitors (e.g., selegiline, rasagiline) are primarily used in the treatment of Parkinson's disease.
By blocking the breakdown of monoamines, their concentration in the synaptic cleft increases, leading to improved mood and enhanced motivation.
Classification of MAO Inhibitors
Irreversible MAO Inhibitors
Classical non-selective MAO inhibitors such as phenelzine and tranylcypromine bind permanently to the enzyme. The body must produce new MAO enzyme before the inhibitory effect subsides. These medications are highly effective but carry a greater risk of interactions.
Reversible MAO Inhibitors (RIMAs)
Moclobemide is a reversible, selective MAO-A inhibitor. It has a more favorable safety profile, as tyramine can displace it from the enzyme binding site when needed, thereby reducing the risk of a hypertensive crisis.
Dosage
The dosage of MAO inhibitors varies depending on the active ingredient and the condition being treated. It must always be determined individually by a physician. Examples include:
- Moclobemide: typically 300–600 mg per day in two divided doses
- Tranylcypromine: 10–30 mg per day (strict medical supervision required)
- Selegiline: 5–10 mg per day (for Parkinson's disease)
Side Effects
MAO inhibitors can cause a range of side effects, including:
- Sleep disturbances and insomnia
- Dizziness and low blood pressure when standing (orthostatic hypotension)
- Weight gain
- Nausea and gastrointestinal complaints
- Sexual dysfunction
- Increased risk of hypertensive crisis with non-selective MAO inhibitors, especially when combined with tyramine-rich foods
Interactions and Dietary Considerations
A particularly important concern when taking non-selective MAO inhibitors is the so-called tyramine interaction. Tyramine is a naturally occurring substance found in certain foods, normally broken down by MAO. When MAO is inhibited, tyramine can cause dangerously high blood pressure (hypertensive crisis). The following foods should be avoided when taking irreversible MAO inhibitors:
- Aged cheeses (e.g., cheddar, camembert)
- Fermented products (e.g., sauerkraut, soy sauce, miso)
- Smoked or pickled meats and fish
- Red wine, beer (especially draft beer)
- Yeast extracts (e.g., Marmite, Vegemite)
In addition, MAO inhibitors can cause dangerous interactions with other medications, including:
- Other antidepressants (e.g., SSRIs, SNRIs) – risk of serotonin syndrome
- Certain pain medications (e.g., tramadol, pethidine)
- Sympathomimetics (e.g., found in cold remedies)
Treatment Context
Today, MAO inhibitors are generally considered second- or third-line treatment options for many indications, as newer antidepressants such as SSRIs and SNRIs offer more favorable side effect and interaction profiles. Nevertheless, MAO inhibitors remain effective and indispensable for certain patient groups – particularly those with treatment-resistant or atypical depression. Their use requires careful medical supervision and patient education regarding dietary restrictions and drug interactions.
References
- American Psychiatric Association (APA): Practice Guideline for the Treatment of Patients with Major Depressive Disorder, 3rd edition (2010).
- Stahl, S. M.: Stahl's Essential Psychopharmacology. Cambridge University Press, 4th edition (2013).
- Shulman, K. I. et al. - Dietary Restrictions and Drug-Drug Interactions with Monoamine Oxidase Inhibitors. Journal of Clinical Psychiatry, 2013.
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