Research shows that common asthma medications called leukotriene receptor antagonists—including montelukast (Singulair)—block the cellular transporters that move folic acid and certain cancer drugs into cells. In laboratory and animal studies, four asthma medications reduced folic acid uptake by 50% at concentrations ranging from 2.34 to 31.8 micromolar, and when mice received asthma medication with folic acid, the folic acid stayed in their bloodstream longer than normal. According to Gram Research analysis, this previously unknown interaction means patients taking both asthma medications and folic acid supplements or cancer treatments should discuss potential dose adjustments with their doctors.
Researchers discovered that common asthma and allergy medications called leukotriene receptor antagonists (LTRAs) may interfere with how your body absorbs and uses folic acid and certain cancer drugs. In laboratory and animal studies, four popular LTRAs—including montelukast (Singulair)—blocked the transporters that move these nutrients into cells. When mice took asthma medication alongside folic acid, the folic acid stayed in their bloodstream longer and didn’t accumulate in the liver as expected. According to Gram Research analysis, these findings suggest people taking both asthma medications and folic acid supplements or cancer treatments should talk to their doctors about potential interactions.
Key Statistics
A 2026 laboratory study found that four leukotriene receptor antagonists (montelukast, zafirlukast, pranlukast, and MK571) blocked folic acid transporters with IC50 values ranging from 2.34 to 31.8 micromolar for one transporter and 2.79 to 45.4 micromolar for another, indicating potent inhibition of nutrient uptake.
In mouse studies, co-administration of montelukast or zafirlukast with folic acid significantly increased folic acid’s time in the bloodstream and prolonged its half-life while reducing its accumulation in the liver, suggesting altered pharmacokinetics of the nutrient.
Research revealed that leukotriene receptor antagonists inhibit the SLC19A1 transporter through a noncompetitive mechanism with inhibition constants of 5.09 to 6.71 micromolar, while inhibiting SLC46A1 through an uncompetitive mechanism with inhibition constants ranging from 4.12 to 95.1 micromolar.
The Quick Take
- What they studied: Whether common asthma medications interfere with how the body transports folic acid and certain cancer drugs into cells
- Who participated: Laboratory cell cultures and mice; no human participants in this initial study
- Key finding: Four asthma medications (montelukast, zafirlukast, pranlukast, and MK571) blocked the cellular transporters that move folic acid and cancer drugs into cells, with effects ranging from mild to strong depending on the medication and transporter
- What it means for you: If you take asthma medication long-term and also use folic acid supplements or certain cancer treatments, your doctor should monitor you more carefully. This doesn’t mean you should stop your asthma medication—just that your healthcare team needs to know about both medications you’re taking
The Research Details
This was a laboratory and animal study published in 2026. Researchers first tested four asthma medications in cell cultures to see if they could block two specific protein transporters (SLC19A1 and SLC46A1) that act like doorways, allowing folic acid and cancer drugs to enter cells. They measured how much the medications blocked these doorways at different concentrations. Then they gave mice either folic acid alone or folic acid combined with asthma medication, and measured how much folic acid ended up in the bloodstream and liver over time.
The researchers used specialized techniques to understand exactly how the asthma medications were blocking these transporters. They discovered that the medications worked differently on each transporter—like using different keys to jam two different locks. This detailed analysis helps explain why the interactions happen and how strong they might be.
Understanding how medications interact with nutrient transporters is crucial for patient safety. Folic acid is essential for cell division and DNA synthesis, while the cancer drugs methotrexate and pemetrexed rely on these same transporters to work. If asthma medications block these doorways, patients might not get enough folic acid or their cancer drugs might not work as well. This research identifies a previously unknown interaction that doctors need to consider when prescribing multiple medications.
This study used rigorous laboratory methods including kinetic analysis to understand the exact mechanisms of interaction. The findings were confirmed in both cell cultures and living animals, which strengthens the results. However, this is early-stage research—it hasn’t been tested in humans yet. The study was published in a peer-reviewed journal, meaning other scientists reviewed it before publication. The lack of human data means we can’t yet say for certain how significant this interaction is in real patients taking these medications.
What the Results Show
All four asthma medications tested (montelukast, zafirlukast, pranlukast, and MK571) blocked both cellular transporters in a dose-dependent manner, meaning stronger effects occurred at higher medication concentrations. For the SLC19A1 transporter, blocking effects ranged from IC50 values of 2.34 to 31.8 micromolar, while for SLC46A1 they ranged from 2.79 to 45.4 micromolar. (These IC50 values represent the concentration needed to block 50% of the transporter’s activity.)
The blocking mechanisms differed between the two transporters. The asthma medications acted as noncompetitive inhibitors of SLC19A1 (meaning they blocked the transporter through a different mechanism than the normal nutrient) with inhibition constants (Ki) ranging from 5.09 to 6.71 micromolar. For SLC46A1, they acted as uncompetitive inhibitors with Ki values ranging from 4.12 to 95.1 micromolar, showing more variability between the different medications.
In the mouse studies, when montelukast or zafirlukast were given together with folic acid, the folic acid stayed in the bloodstream longer (increased AUC and Cmax values) and took longer to clear from the body (prolonged half-life). Importantly, the folic acid accumulated less in the liver than expected, suggesting the asthma medications were preventing normal folic acid uptake into liver cells.
The study also tested how the asthma medications affected the transport of methotrexate and pemetrexed, which are cancer drugs that use the same cellular doorways as folic acid. Both cancer drugs showed similar blocking patterns to folic acid, suggesting that patients taking asthma medications might experience altered levels of these cancer drugs in their bodies. The consistency of effects across different drugs and different asthma medications suggests this is a broad class effect rather than something unique to one medication.
This appears to be the first study to identify this specific interaction between leukotriene receptor antagonists and folate transporters. Previous research has documented that LTRAs can interact with other drug transporters, but this particular mechanism involving SLC19A1 and SLC46A1 was previously unrecognized. The findings add to growing evidence that asthma medications have broader effects on cellular transport systems than previously understood.
This study has several important limitations. First, it was conducted in laboratory cells and mice, not in humans, so we don’t know if the same interactions occur in people taking these medications. Second, the study didn’t measure actual clinical outcomes—we don’t know if these transporter interactions cause real health problems in patients. Third, the sample size for animal studies wasn’t specified. Fourth, the study only looked at four specific LTRAs; other asthma medications in this class weren’t tested. Finally, the study didn’t examine how long-term use of these medications together might affect folic acid status or cancer drug effectiveness in real patients.
The Bottom Line
Based on this research, people taking long-term asthma medications (especially montelukast or zafirlukast) who also need folic acid supplements or cancer treatments should inform their doctors about all medications they’re taking. Doctors may want to monitor folic acid levels more frequently or adjust doses. However, this recommendation is based on laboratory and animal evidence, not human studies, so confidence is moderate. Do not stop taking asthma medication without medical guidance—these medications are important for controlling asthma and allergies.
This research is most relevant to: (1) people with asthma or allergies taking LTRAs long-term, especially if they also take folic acid supplements; (2) cancer patients taking methotrexate or pemetrexed who also use asthma medications; (3) healthcare providers prescribing multiple medications to the same patient; (4) pregnant women taking LTRAs (since folic acid is critical during pregnancy). People taking asthma inhalers occasionally rather than daily are less likely to be affected.
Since this is early-stage research, we don’t yet know how quickly interactions would develop or how long they would last. In the mouse studies, effects were observed within the timeframe of the experiment, but human studies would be needed to determine realistic timelines for clinical effects. Any changes in folic acid status or medication effectiveness would likely develop gradually over weeks to months of concurrent use.
Frequently Asked Questions
Can asthma medication affect how my body uses folic acid?
Research suggests that leukotriene receptor antagonists like montelukast may block the cellular transporters that move folic acid into cells. In animal studies, this caused folic acid to stay in the bloodstream longer. Talk to your doctor if you take both asthma medication and folic acid supplements.
Should I stop taking my asthma medication if I’m also taking folic acid?
No—do not stop asthma medication without medical guidance. Instead, inform your doctor that you’re taking both medications. Your doctor may monitor your folic acid levels more closely or adjust doses to ensure you’re getting adequate nutrition while managing your asthma effectively.
Does this interaction affect cancer patients taking methotrexate?
Laboratory studies suggest asthma medications may also block the transporters that methotrexate uses to enter cells. Cancer patients taking both methotrexate and asthma medications should definitely discuss this with their oncologist, who may need to adjust dosing or monitoring strategies.
How long does it take for this drug interaction to cause problems?
This study was conducted in laboratory cells and mice, not humans, so we don’t yet know how quickly problems would develop in people. Effects would likely develop gradually over weeks to months of taking both medications together. Regular monitoring by your doctor is important.
Which asthma medications cause this folic acid interaction?
This study tested four leukotriene receptor antagonists: montelukast (Singulair), zafirlukast (Accolate), pranlukast, and MK571. All four blocked folic acid transporters in laboratory studies. Other asthma medications in this class weren’t tested, so talk to your doctor about your specific medications.
Want to Apply This Research?
- Track daily asthma medication use (type and dose) alongside folic acid supplement intake or cancer drug administration dates. Note any changes in energy levels, appetite, or symptoms that might indicate altered nutrient absorption.
- If you take both asthma medication and folic acid or cancer drugs, set a reminder to discuss this combination with your doctor at your next appointment. Keep a medication log showing all prescriptions, supplements, and over-the-counter products you’re taking to share with your healthcare provider.
- Long-term, monitor for signs of folic acid deficiency (fatigue, weakness, shortness of breath) or changes in cancer treatment effectiveness. Schedule regular check-ins with your doctor to review all medications together. If your doctor orders blood work, ask specifically about folic acid levels if you’re taking both asthma and folic acid medications.
This research is preliminary and based on laboratory and animal studies, not human clinical trials. The findings have not yet been confirmed in people taking these medications. This information is for educational purposes and should not replace professional medical advice. If you take asthma medications and folic acid supplements, cancer drugs, or are pregnant, consult your healthcare provider before making any changes to your medication regimen. Do not stop taking prescribed asthma medication without medical guidance. Your doctor can assess your individual risk and determine whether monitoring or dose adjustments are necessary based on your specific situation.
This research translation is published by Gram Research, the science division of Gram, an AI-powered nutrition tracking app.
