What to Know About Marplan Side Effects Before You Start

Starting a new antidepressant always comes with questions, and if your doctor has prescribed Marplan (Isocarboxazid), you probably have more questions than usual. Marplan is a monoamine oxidase inhibitor (MAOI) — a powerful but older class of antidepressant that works differently from the SSRIs and SNRIs most people try first.

Because it works differently, it also has a unique side effect profile. Some side effects are mild and temporary. Others are serious and require immediate medical attention. This guide covers both, so you know exactly what to watch for.

What Is Marplan?

Marplan is the brand name for Isocarboxazid, a non-selective, irreversible MAOI made by Validus Pharmaceuticals. It's FDA-approved for treatment-resistant major depressive disorder — meaning it's typically prescribed after other antidepressants haven't worked. It comes as a 10 mg oral tablet, and most people take 20–60 mg per day in divided doses.

Common Side Effects of Marplan

These side effects are the ones most people experience, especially during the first few weeks. They're usually mild and often improve as your body adjusts to the medication.

• Dizziness — One of the most common complaints. May worsen when standing up quickly (orthostatic hypotension).
• Headache — Mild to moderate headaches are common early on. However, a sudden severe headache could signal a hypertensive crisis (see below).
• Nausea — Usually mild and improves within the first week or two.
• Dry mouth — A frequent side effect. Sugar-free gum and staying hydrated can help.
• Drowsiness — Some people feel sedated, especially at higher doses.
• Insomnia — Others experience the opposite — trouble falling or staying asleep.
• Tremor — Mild shaking, usually in the hands.
• Constipation — Increasing fiber and water intake usually helps.
• Increased appetite and weight gain — MAOIs are known for this. Monitor your weight and talk to your doctor if it becomes a concern.
• Sexual dysfunction — Including decreased libido, difficulty with arousal, and delayed orgasm.

Most of these side effects are manageable and tend to lessen over time. If any become severe or don't improve after a few weeks, tell your doctor.

Serious Side Effects: When to Seek Help Immediately

Marplan carries some serious risks that require immediate attention. Knowing these in advance can potentially save your life.

Hypertensive Crisis

This is the most dangerous risk with Marplan. A hypertensive crisis happens when your blood pressure spikes to dangerously high levels, usually because of an interaction with tyramine-containing foods or certain medications.

Symptoms include:

• Sudden, severe headache (often at the back of the head)
• Rapid heartbeat or heart pounding
• Neck stiffness
• Nausea and vomiting
• Sweating (sometimes with fever or cold, clammy skin)
• Dilated pupils
• Chest pain

If you experience these symptoms, go to the emergency room immediately. A hypertensive crisis can cause stroke, brain hemorrhage, or death if untreated.

Serotonin Syndrome

This occurs when too much serotonin builds up in your body, usually from combining Marplan with other serotonergic drugs (SSRIs, SNRIs, Triptans, Dextromethorphan, etc.).

Symptoms include:

• Agitation and restlessness
• Confusion
• Rapid heart rate
• High blood pressure
• Muscle rigidity or twitching
• Diarrhea
• Fever

Serotonin syndrome is a medical emergency. Call 911 or go to the ER immediately.

Suicidal Thoughts or Behavior

Marplan carries an FDA boxed warning — the most serious type — about increased risk of suicidal thinking and behavior, especially in children, adolescents, and young adults. While Marplan is not approved for children, this risk applies to young adults as well.

Contact your doctor immediately or call 988 (Suicide & Crisis Lifeline) if you experience worsening depression, new or worsening anxiety, agitation, panic attacks, or thoughts of self-harm.

Liver Problems (Hepatotoxicity)

Marplan can affect your liver. Your doctor should order baseline liver function tests and monitor them periodically. Seek medical attention if you notice:

• Yellowing of skin or eyes (jaundice)
• Dark urine
• Severe fatigue
• Upper right abdominal pain

Other Serious Side Effects

• Severe hypotension — Blood pressure drops that cause fainting.
• Seizures — Rare but possible.
• Mania or hypomania — Especially in patients with undiagnosed bipolar disorder.

Special Populations

Older Adults

Elderly patients are more susceptible to orthostatic hypotension (dizziness when standing). Falls are a real concern. Your doctor may start at a lower dose and increase more slowly.

Pregnancy and Breastfeeding

Marplan is contraindicated during pregnancy. It should not be used while breastfeeding. If you're planning to become pregnant, talk to your doctor about transitioning to a safer medication well in advance.

Young Adults (18–24)

Because of the increased risk of suicidal thoughts and behavior, young adults should have more frequent follow-up appointments — especially during the first few months of treatment or after dose changes.

How to Manage Marplan Side Effects

Here are practical tips for the most common issues:

• Dizziness: Stand up slowly from sitting or lying positions. Stay hydrated.
• Dry mouth: Chew sugar-free gum, suck on ice chips, and drink water throughout the day.
• Constipation: Eat high-fiber foods, drink plenty of water, and consider a gentle stool softener (check with your doctor first).
• Insomnia: Take your last dose earlier in the day. Practice good sleep hygiene.
• Weight gain: Monitor your diet and exercise. Talk to your doctor if it becomes significant.
• Sexual side effects: Don't stop taking Marplan without talking to your doctor. There may be dosage adjustments or other strategies that help.

The most important thing you can do is follow the tyramine-restricted diet carefully and avoid all contraindicated medications. Most of the life-threatening side effects of Marplan are caused by interactions, not the drug alone. Review our complete guide to Marplan drug interactions for the full list.

Final Thoughts

Marplan is a powerful antidepressant that can be life-changing for people with treatment-resistant depression. But it demands respect. The side effects are real, and some are dangerous. The good news: most serious side effects are preventable if you follow the dietary rules and avoid drug interactions.

Work closely with your psychiatrist, keep your follow-up appointments, and don't hesitate to call if something feels off. If you need help finding Marplan in stock, Medfinder can help you locate a pharmacy near you.