A documented moderate interaction exists between montelukast (a leukotriene receptor antagonist used for asthma and allergies) and gemfibrozil (a fibrate used to lower triglycerides and cholesterol). When taken together, gemfibrozil can increase the amount of montelukast in your body, and a dosing reduction of montelukast may be required. This is not a reason to avoid either medication if both are medically necessary, but it does require monitoring and conversation with your pharmacist or physician before starting or continuing both drugs.
According to drug interaction information sourced from NIH/NLM clinical data, this interaction is classified as moderate in severity. The documented mechanism is that gemfibrozil acts as a strong inhibitor of an enzyme called CYP2C8, which is responsible for breaking down (metabolizing) montelukast in the body. When gemfibrozil blocks this enzyme, montelukast clears more slowly and accumulates to higher levels in the bloodstream.
The source record states: "Gemfibrozil is a strong CYP2C8 inhibitor that may increase montelukast exposure; dosing reduction may be required."
This information comes from comprehensive drug labeling and interaction databases maintained by the National Library of Medicine (NLM), which aggregate FDA-approved product labeling and clinical evidence. The interaction was last reviewed and updated on May 4, 2026.
Your liver contains many enzymes whose job is to break down medications so your body can eliminate them. One of these enzymes is called cytochrome P450 2C8, or CYP2C8 for short. Montelukast depends on this enzyme to be metabolized and removed from your body at the appropriate rate.
Gemfibrozil works partly as a medication for lowering cholesterol and triglycerides, but it also has the property of strongly inhibiting (blocking or slowing) the CYP2C8 enzyme. This means that when you take both drugs, the enzyme that normally breaks down montelukast is less active, so montelukast stays in your body longer and builds up to higher concentrations.
"Increased montelukast exposure" is a pharmacology term meaning that the amount of montelukast in your blood is higher, and it remains elevated for longer, than it would if you were taking montelukast alone. This higher exposure can potentially lead to side effects or therapeutic imbalance if not managed.
The source record indicates that a dosing reduction of montelukast may be needed to counteract this buildup and keep montelukast levels in a safe therapeutic range. However, the supplied source record does not specify a particular dose adjustment, which means any dose change must be determined by your individual prescriber based on your specific clinical situation, kidney and liver function, and other medications.
The interaction is classified as moderate rather than severe or contraindicated because:
A severe or contraindicated interaction would suggest that the drugs should not be used together or only under extreme circumstances; that is not the case here.
Anyone taking both montelukast and gemfibrozil should be aware of this interaction and inform their pharmacist and physician. There is no specific patient subgroup identified in the source record, but general principles apply:
The following is a hypothetical scenario illustrating the documented interaction. It is not a real case and does not represent actual patient data.
Imagine a 58-year-old patient with both asthma (treated with montelukast 10 mg once daily) and elevated triglycerides (treated with atorvastatin). A recent blood test shows that triglycerides remain high, so the physician adds gemfibrozil 600 mg twice daily. Three weeks later, the patient reports feeling tired and notices some mild gastrointestinal discomfort.
The pharmacist reviews the addition of gemfibrozil and recognizes that gemfibrozil inhibits CYP2C8, which metabolizes montelukast. The accumulation of montelukast due to enzyme inhibition could contribute to the patient's symptoms. The pharmacist alerts the physician, who may then consider reducing the montelukast dose from 10 mg once daily to 5 mg once daily, or ordering a montelukast blood level (if available), while continuing close monitoring. This hypothetical adjustment would be made based on the patient's individual tolerance and response, not automatically.
Again, this is a hypothetical illustration of how the documented interaction might be managed proactively.
A 62-year-old patient with asthma and high triglycerides is seeing a pulmonologist for asthma control and a cardiologist for lipid management. The cardiologist is considering starting gemfibrozil because diet and statins have not sufficiently lowered triglycerides. Before starting gemfibrozil, the cardiologist checks the patient's medication list, notes the montelukast, and consults with the primary care physician. Together, they decide to start gemfibrozil at the standard dose and proactively reduce montelukast from 10 mg to 5 mg once daily, anticipating the CYP2C8 inhibition. The patient is monitored at follow-up visits to ensure asthma control remains adequate on the lower montelukast dose and triglycerides improve on gemfibrozil. If asthma control worsens, the dose of montelukast can be adjusted upward in small increments under supervision.
If you are taking both montelukast and gemfibrozil, or if you are considering starting one while already on the other, here are important points to raise with your healthcare provider:
Do not change or stop either medication on your own. Any dose adjustment or medication change should be made by your prescriber based on your individual medical situation.
If you are currently taking montelukast, gemfibrozil, or any other medications, use checkdruginteractions.com to check your complete medication list for documented interactions. Enter all of your prescription drugs, over-the-counter medications, and supplements to identify any potential interactions. This tool is a starting point for an informed conversation with your pharmacist or physician—use it to ask better questions and ensure your medication regimen is as safe and effective as possible. Always confirm medication decisions, including dose changes or new prescriptions, with a licensed pharmacist or physician before making any changes.
CDI checks every pair across up to 20 drugs — backed by FDA and NIH data.
Drug interaction data sourced from U.S. FDA drug labeling via openFDA and the U.S. National Library of Medicine (NLM), National Institutes of Health. For informational purposes only. Always consult your pharmacist or physician before making any medication decisions.
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