See also How to Use section.

Drug interactions may change how your medications work or increase your risk for serious side effects. This document does not contain all possible drug interactions. Keep a list of all the products you use (including prescription/nonprescription drugs and herbal products) and share it with your doctor and pharmacist. Do not start, stop, or change the dosage of any medicines without your doctor's approval.

Some products that may interact with this drug include: other antidepressants (including maprotiline, mirtazapine, nefazodone, TCAs such as amitriptyline/nortriptyline), appetite suppressants (such as diethylpropion), drugs for attention deficit disorder (such as atomoxetine, methylphenidate), apraclonidine, bupropion, buspirone, carbamazepine, cyclobenzaprine, deutetrabenazine, dextromethorphan, certain drugs for high blood pressure (such as guanethidine, methyldopa, beta blockers such as atenolol, clonidine, rauwolfia alkaloids), other MAO inhibitors (linezolid, metaxalone, methylene blue, moclobemide, phenelzine, procarbazine, rasagiline, safinamide, selegiline, tranylcypromine), metoclopramide, certain opioid medications (such as fentanyl, methadone, tapentadol), certain drugs for Parkinson's (such as entacapone, levodopa, tolcapone), street drugs (such as LSD, mescaline), stimulants (such as amphetamines, cocaine, dopamine, epinephrine, phenylalanine), tetrabenazine, "triptan" migraine drugs (such as sumatriptan, rizatriptan), tramadol, tyrosine, tryptophan, valbenazine.

The risk of serotonin syndrome/toxicity increases if you are also taking other drugs that increase serotonin. Examples include street drugs such as MDMA/ "ecstasy," St. John's wort, certain antidepressants (including SSRIs such as fluoxetine/paroxetine, SNRIs such as duloxetine/venlafaxine), meperidine, among others. The risk of serotonin syndrome/toxicity may be more likely when you start or increase the dose of these drugs.

Tell your doctor or pharmacist if you are using any of these medications before, during, or within 2 weeks after treatment with isocarboxazid. Tell your doctor or pharmacist if you have taken fluoxetine during at least 5 weeks before starting isocarboxazid. Discuss with your doctor how much time to wait between starting or stopping any of these drugs and taking isocarboxazid.

Tell your doctor or pharmacist if you are taking other products that cause drowsiness such as opioid pain or cough relievers (such as codeine, hydrocodone), alcohol, marijuana (cannabis), drugs for sleep or anxiety (such as alprazolam, lorazepam, zolpidem), muscle relaxants (such as carisoprodol, cyclobenzaprine), or antihistamines (such as cetirizine, diphenhydramine).

Check the labels on all your medicines (such as allergy, cough-and-cold products, diet pills) because they may contain dextromethorphan, decongestants, stimulants, or ingredients that cause drowsiness. Ask your pharmacist about the safe use of those products.