Isocarboxazid (Marplan)

How Medicare covers it

Part D (forms used at home). Part A during a covered inpatient stay. No Part B clinician-administered form in the CMS Part B spending file.

What it treats

Treatment of depression. Because of its potentially serious side effects, Marplan is not an antidepressant of first choice in newly diagnosed patients — it is reserved for depressed patients who have not responded satisfactorily to other antidepressant drugs. Its effectiveness was shown in 6-week trials in outpatients with major depressive disorder, often with anxiety symptoms; effectiveness in long-term use (more than 6 weeks) has not been systematically evaluated.

What it is for, in depth

Marplan (isocarboxazid) is one of the original MAO inhibitor antidepressants, used to treat major depression — but deliberately not as a first choice. The label reserves it for patients who have not responded satisfactorily to other antidepressants, because MAOIs carry risks the common antidepressants do not: tyramine in foods like aged cheese and fermented drinks can no longer be broken down, so blood pressure can spike to a life-threatening hypertensive crisis, and the drug interacts dangerously with most other antidepressants, many pain and cold medicines, and anesthetics. It is taken as 10 mg tablets, starting at 10 mg twice a day and building to a maximum of 60 mg a day in divided doses, with benefit taking 3 to 6 weeks. It also carries the antidepressant class boxed warning about suicidal thinking in children, adolescents, and young adults, and it is not approved for children. Patients get a food and medicine avoidance list and carry it seriously for the whole course of treatment.

How it works

Marplan is a non-selective hydrazine monoamine oxidase inhibitor (MAOI): it blocks the enzyme monoamine oxidase in the brain, heart, and liver. The label states it is thought to work by raising brain levels and effects of biogenic amines (such as serotonin, norepinephrine, and dopamine), though the exact antidepressant mechanism is not completely understood. That same enzyme block is why so many foods and drugs interact with it.

How it is taken

10 mg tablets by mouth, scored, supplied in bottles of 100. The starting dose is 10 mg twice a day. If tolerated, the dose is increased by 10 mg every 2 to 4 days to reach 40 mg a day by the end of the first week, then by up to 20 mg a week to the maximum recommended dose of 60 mg a day, split into 2 to 4 doses a day. Once the best response is reached, the dose is reduced slowly over several weeks to the lowest level that maintains the response. Benefit may take 3 to 6 weeks, and doses above 40 mg a day are used with caution because experience is limited.

Common side effects

['Dizziness (29% at doses under 50 mg/day — the most common in the trials)', 'Headache (15%)', 'Dry mouth (9%)', 'Constipation (7%)', 'Nausea (6%)', 'Sleep disturbance (5%)']

Serious warnings

['Hypertensive crisis — the most important reaction with MAO inhibitors; triggered by tyramine foods or interacting drugs, with symptoms such as occipital headache, palpitations, neck stiffness, nausea, vomiting, sweating, and light sensitivity; it is sometimes fatal and intracranial bleeding has been reported. Marplan is stopped if palpitations or frequent headaches occur during therapy', 'Clinical worsening and suicide risk (boxed warning) — monitor all patients closely, especially early in treatment', 'Hypotension, including postural (standing) hypotension, which can cause fainting', 'Hepatotoxicity — a low incidence of altered liver function and jaundice; periodic liver function tests are advised', 'Lowered seizure threshold in epileptic patients', 'Second-line status — because of potentially serious side effects, Marplan is not an antidepressant of first choice and should be reserved for patients who have not responded to other antidepressants', 'MAOIs can mask the warning pain of angina, and can contribute to hypoglycemia in diabetic patients on insulin or oral hypoglycemics', 'Activation of mania or hypomania has been reported with antidepressants; screen for bipolar disorder before starting (Marplan is not approved for bipolar depression)']

Boxed warning

Antidepressants increase the risk of suicidal thinking and behavior (suicidality) in children, adolescents, and young adults, compared with placebo, in short-term studies of major depressive disorder and other psychiatric disorders. Anyone considering the use of Marplan or any other antidepressant in a child, adolescent, or young adult must balance this risk with the clinical need. There was no increase in risk with antidepressants compared to placebo in adults beyond age 24, and there was a reduction in risk at ages 65 and older. Depression and certain other psychiatric disorders are themselves associated with increases in suicide risk. Patients of all ages who start antidepressant therapy should be monitored closely for clinical worsening, suicidality, or unusual changes in behavior, and families and caregivers should be advised of the need for close observation and communication with the prescriber. Marplan is not approved for use in pediatric patients.

Who should be careful

['People with hypersensitivity to isocarboxazid, a confirmed or suspected cerebrovascular defect, cardiovascular disease, hypertension, or a history of headache — contraindicated per the label', 'People with pheochromocytoma — contraindicated', 'People with a history of liver disease or abnormal liver function tests — contraindicated', 'People with severe renal impairment — contraindicated; milder renal impairment also calls for caution because the drug may accumulate', 'Children and adolescents under 16 — not recommended; safety and effectiveness have not been established, and Marplan is not approved for pediatric use', 'People with diabetes on insulin or oral hypoglycemic agents, epilepsy, hyperthyroidism, or hyperactive/agitated or schizophrenic presentations — extra caution', 'Pregnant or breastfeeding women — use only if clearly needed; safety in pregnancy has not been adequately evaluated', 'Anyone scheduled for elective surgery or dental work — Marplan must be stopped at least 10 days beforehand and sympathomimetic anesthetics avoided']

Major interactions

['Other MAO inhibitors and dibenzazepine (tricyclic) antidepressants — reactions include hypertensive crisis, seizures, coma, and circulatory collapse; allow at least 1 week between stopping one and starting another, and start at half the usual dose', 'SSRIs and other serotonergic drugs — serious, sometimes fatal serotonin-type reactions; no SSRI within 14 days of Marplan (5 weeks after fluoxetine, 2 weeks after sertraline or paroxetine), and wait at least 10 days after stopping Marplan before starting an SSRI', 'Bupropion — contraindicated; at least 14 days must pass between stopping bupropion and starting Marplan', 'Buspirone — blood pressure increases have been reported', 'Sympathomimetic drugs, including amphetamines and over-the-counter cold, hay fever, and weight-reduction products containing vasoconstrictors — hypertensive crisis risk; also guanethidine, methyldopa, methylphenidate, reserpine, epinephrine, levodopa, and tryptophan', 'Meperidine — contraindicated, including within 2 to 3 weeks after stopping an MAOI; excitement, seizures, coma, respiratory depression, and death have been reported', 'Dextromethorphan (in many cough medicines) — brief episodes of psychosis and bizarre behavior have been reported', 'Foods high in tyramine — aged cheeses, Chianti, sherry, beer (including non-alcoholic), pickled herring, liver, dry sausage, soy sauce, sauerkraut, fava or broad bean pods, and yeast extracts can trigger hypertensive crisis', 'Anesthetics — no elective surgery with general anesthesia while on Marplan; stop it at least 10 days before elective surgery; avoid cocaine and local anesthetics containing sympathomimetic vasoconstrictors', 'CNS depressants, including narcotics, barbiturates, and alcohol — effects are increased', 'Antihypertensive drugs, including thiazide diuretics — marked extra blood-pressure lowering (hypotension)', 'Excessive caffeine, and disulfiram (use with caution)']

Cost and saving notes

Isocarboxazid (Marplan) is a brand-only tablet that every Part D plan in the 2027 data lists, most often on Tier 4, the non-preferred brand tier, so expect a higher copay or coinsurance and possibly prior authorization. If the cost is a problem, ask your plan about a tier exception and check whether Extra Help applies to you. The 2027 Part D out-of-pocket cap is $2,400 for the year, and the Medicare Prescription Payment Plan can spread that cost across the year.

Why it is in its tier

Isocarboxazid (Marplan) sits on Tier 4 in 90.54% of the plans that list it (4975 of 5495 listing plans). Tier 4 is the non-preferred tier — higher copays or coinsurance. The data-visible drivers: It is a brand-only product with no generic version in the formulary data, and the CMS dashboard puts its average Part D spending at about $4,158 per beneficiary for 2024 — a mid-cost drug, which matches where plans place it. It is listed by 100.0% of Part D plans. The tier shown is the most common one; individual plans vary.

Sources

• MARPLAN (ISOCARBOXAZID) TABLET [LIFSA DRUGS LLC] — DailyMed
• MedlinePlus — National Library of Medicine
• MedlinePlus Drug Information

What official patient guides say

Isocarboxazid (Marplan) comes as a tablet to take by mouth, usually between two and four times a day at around the same times every day, swallowed with water or another liquid (if you are unable to swallow the tablets, you can crumble them and swallow the crumbled tablets with food or liquid), and it may take 3 to 6 weeks or longer before you feel its full benefit, so continue taking it if your symptoms improve and do not stop without talking to your doctor; during treatment you must follow strict dietary instructions — you may experience a serious reaction if you eat foods high in tyramine, including meat, poultry, fish, or cheese that has been smoked, aged, improperly stored, or spoiled, certain fruits, vegetables, and beans, alcoholic beverages, and fermented yeast products, so follow your doctor's or dietitian's directions about which foods to avoid completely and which you may eat in small amounts, and also avoid foods and drinks that contain caffeine. If you forget a dose, take the missed dose as soon as you remember it, but if it has been more than 2 hours since you were supposed to take the dose, skip the missed dose and continue your regular dosing schedule — do not take a double dose to make up for a missed one. Keep the medication in the container it came in, tightly closed and out of reach of children, stored at room temperature and away from excess heat and moisture (not in the bathroom), and keep all appointments with your doctor and the laboratory, as your doctor will check your blood pressure often and will order certain lab tests to check your body's response to isocarboxazid.

Source: MedlinePlus Drug Information

Part D formulary coverage

Source: CMS Prescription Drug Plan Formulary, Pharmacy Network, and Pricing Information Files — Monthly file 2026-10-15 (plan year 2027), file 2027_20261008.zip (data.cms.gov dataset ed1496ea-23e7-41f1-9292-172fa842ccfb): basic drugs formulary file + plan information file, both dated 20261031 inside the zip; downloaded and aggregated 2026-10-30. Medication RxCUI sets resolved through the NLM RxNav (RxNorm) API.

What you pay

A tier is not a price; what you pay depends on your plan, pharmacy, and benefit stage; Extra Help or Medicaid can lower it further.

Sources: CMS Plan Benefit Package + formulary data; CMS NADAC · Checked 2026-11-07

Coverage by plan and tier

Of the 5,495 Medicare drug plans we track for 2027, 5,495 list Isocarboxazid (Marplan) — 100% of plans. Most of those plans put it on Tier 4: 4,975 plans, 90.5% of the plans that list it. Other plans place it on Tier 3 (359 plans), Tier 1 (123 plans) or Tier 2 (38 plans). For example: Aetna Medicare Dual Extra (HMO D-SNP) puts it on Tier 4; Aetna Medicare Dual Extra Care (PPO D-SNP) puts it on Tier 4; Aetna Medicare Value Plus (PPO) puts it on Tier 4. You can compare these plans side by side on our Medicare Advantage hub. A tier is not a price. What you pay also depends on whether you have met your plan';s deductible, whether the drug costs a flat copay or a share of the price, and whether you get Extra Help or Medicaid.

Read next

• Part D in 2027: The $700 Deductible, the $2,400 Cap, and the $35 Insulin Rule
• Extra Help in 2027: Lower Drug Copays and Who Qualifies
• Checking Medicare Savings Programs and Extra Help

Part D spending averages (2024)

Source: CMS Medicare Part D Spending by Drug (Drug Spending Dashboard), release RY26 P04 V10, data through 2024 (DSD_PTD_RY26_P04_V10_DY24_BGM.csv), downloaded 2026-10-30

Companies covering this drug

Part D and Medicare Advantage plan sponsors that list this drug on a formulary, 50 at a time.