Montelukast Drug Interactions: What to Avoid and What to Tell Your Doctor

Montelukast has a relatively clean drug interaction profile compared to many other prescription medications — it does not broadly inhibit the cytochrome P450 enzyme system the way some drugs do. However, there are several important interactions and precautions patients and providers should know about before starting or continuing montelukast therapy.

How Montelukast Is Metabolized

Montelukast is primarily metabolized by two liver enzymes in the cytochrome P450 system: CYP3A4 and CYP2C8. It is also a weak inhibitor of CYP2C8 in laboratory studies — but clinical studies have shown this doesn't significantly affect drugs metabolized by CYP2C8 in real patients, likely because montelukast is so strongly protein-bound (>99%).

The key interaction concern with montelukast is drugs that strongly induce CYP3A4 and/or CYP2C8 — these can significantly reduce montelukast levels in the blood, making it less effective.

Significant Drug Interactions

1. CYP Enzyme Inducers (Moderate Severity)

These medications strongly increase liver enzyme activity and break down montelukast faster than normal, reducing its blood levels:

Phenobarbital — anticonvulsant; reduces montelukast AUC (overall blood exposure) by approximately 40% following a single 10 mg dose. Clinical monitoring is recommended when used together. No dose adjustment is generally required, but lack of efficacy should be watched for.

Rifampin (Rifadin) — antibiotic used for tuberculosis; a potent CYP enzyme inducer that significantly increases montelukast metabolism. Clinical monitoring for loss of asthma or allergy control is important during and after rifampin therapy.

Carbamazepine (Tegretol) — anticonvulsant and mood stabilizer; another CYP inducer that may reduce montelukast levels. Monitor for reduced efficacy.

St. John's Wort (herbal supplement) — a CYP3A4 inducer; may reduce montelukast efficacy. Many patients don't consider herbal supplements "medications" — always ask about them.

2. Aspirin and NSAIDs (Special Caution)

Montelukast does not directly interact with aspirin or non-steroidal anti-inflammatory drugs (NSAIDs) in a pharmacokinetic sense. However, patients with aspirin-sensitive asthma (a subtype of asthma where aspirin and NSAIDs trigger severe bronchospasm) should continue to avoid these drugs while on montelukast. Montelukast does not provide complete protection against aspirin-induced bronchospasm in sensitive patients.

3. Gemfibrozil (Lopid) — Increases Montelukast Exposure

Gemfibrozil is a fibrate used to treat high triglycerides. It inhibits CYP2C8 and can increase montelukast blood levels, potentially increasing both efficacy and the risk of side effects. Clinical significance is uncertain but monitoring is prudent when these drugs are used together.

Drugs Montelukast Does NOT Significantly Interact With

Montelukast was used concomitantly with many common medications in clinical trials without clinically significant interactions. These include:

Warfarin (Coumadin) — no effect on prothrombin time or INR

Oral contraceptives (norethindrone/ethinyl estradiol) — no clinically significant effect

Prednisone and prednisolone (corticosteroids) — no clinically significant effect

Thyroid hormones — no significant interaction

Benzodiazepines — no significant interaction

Decongestants — no significant interaction

Terfenadine (antihistamine) — no significant effect on plasma levels

Neuropsychiatric Drug Interactions (Additive Risk)

While not a direct pharmacokinetic interaction, patients who take montelukast alongside other medications with neuropsychiatric effects (antidepressants, sedatives, anxiolytics) should be monitored more closely. The FDA's black box warning for montelukast highlights suicidal ideation, depression, and behavioral changes as potential side effects. If a patient is already on psychiatric medications, adding montelukast requires careful monitoring for additive effects on mood and behavior.

What to Tell Your Doctor Before Starting Montelukast

Before your prescriber writes the montelukast prescription, make sure they know about:

All current prescription medications, including anticonvulsants, antibiotics, and lipid-lowering drugs

All OTC medications (especially ibuprofen, aspirin, naproxen if you have aspirin-sensitive asthma)

All herbal supplements (especially St. John's Wort, which is commonly not reported as a "medication")

Any history of depression, anxiety, suicidal ideation, or other psychiatric conditions

Phenylketonuria (PKU) if you'll be taking chewable tablets or granules (contain aspartame)

For a full overview of montelukast side effects, see our guide: Montelukast Side Effects: What to Expect. And if you need help finding montelukast in stock near you, medfinder can search local pharmacies on your behalf.