What Should I Do If I Accidentally Took Two Montelukast?

An accidental double dose of montelukast is overwhelmingly unlikely to cause you any harm. Montelukast has one of the widest safety margins of any commonly prescribed medication: poison control data show that even children who accidentally swallowed doses many times the normal amount almost never experienced anything worse than a stomachache. That said, knowing exactly what to expect, what to watch for, and how to avoid repeating the mistake is worth a few minutes of your time.

The Safety Margin Is Remarkably Wide

The standard adult dose of montelukast is 10 mg taken once daily. If you accidentally took two tablets, you ingested 20 mg. To put that in perspective, a large analysis of pediatric montelukast exposures reported to poison control centers in Texas found that children who swallowed doses as high as 536 mg, more than 50 times the adult dose, did not experience serious adverse effects. About 95 percent of cases in that dataset showed no observable effect at all, and the remaining cases were classified as minor.¹

A separate 17-year study covering over 17,000 single-dose montelukast exposures in children aged five to seventeen found similar results. Even among the 618 cases classified as “ultra-high-dose” exposures (50 mg or more), no serious or life-threatening events were reported, no one needed CPR, and there were no deaths.² Your accidental 20 mg dose sits well within the range that these large datasets have repeatedly found to be clinically inconsequential.

Symptoms You Might Actually Feel

Most people who take a double dose feel nothing unusual at all. When symptoms do appear after a montelukast overdose, the most commonly reported one is abdominal pain, essentially a stomachache. In the 17-year analysis of pediatric exposures, abdominal pain occurred in about 0.23 percent of all cases but rose to roughly 1.5 percent among those who took very high doses.² Other infrequently reported symptoms in overdose include mild headache, thirst, drowsiness, and hyperactivity in children. These tend to resolve on their own without treatment.

If you do develop stomach discomfort, it should pass within a few hours. Drinking water and eating something bland can help. You do not need to induce vomiting, take activated charcoal, or do anything dramatic. In the vast majority of overdose cases tracked by poison control, the person was managed at home with no medical intervention needed at all.¹

What You Should Do Right Now

If you just realized you took two montelukast tablets, here is the practical checklist:

Do not panic: The data strongly suggest that a double dose is safe for both adults and children.
Skip your next dose: Simply resume your normal schedule at the next regular time. Do not try to “make up” for the extra by skipping two doses, just skip one.
Note the time: If any mild symptoms develop, knowing when you took the extra tablet helps if you end up speaking with a pharmacist or nurse line.
Call Poison Control if you are worried: In the United States, the number is 1-800-222-1222. They field calls about montelukast frequently and can give advice specific to your situation. In the 17-year pediatric dataset, about 96 percent of exposures were managed without needing to visit a healthcare facility.²
Seek emergency care only if unusual symptoms appear: Difficulty breathing, chest pain, severe allergic reaction, or any symptom that feels genuinely alarming warrants a call to emergency services. These are not expected from a montelukast double dose, but they are always reasons to seek help regardless of the cause.

How Quickly Your Body Clears the Extra Dose

Montelukast is absorbed relatively quickly after you swallow it, reaching peak blood levels in roughly three to four hours. Its half-life, the time it takes your body to clear half the drug from your bloodstream, is about five hours in healthy adults.³ That means by the time you wake up the morning after an evening double dose, most of the extra drug has already been processed and eliminated.

Your liver does the heavy lifting here. The enzyme primarily responsible for breaking down montelukast is CYP2C8, which handles roughly 72 to 80 percent of the drug’s metabolism.⁴ A smaller portion is processed by CYP2C9 and CYP3A4. The practical upshot is that your body has a well-established and efficient pathway for clearing montelukast, and a single extra 10 mg tablet does not overwhelm that system.

Bioavailability of the tablet form is about 66 percent, meaning a third of what you swallow never reaches your bloodstream in the first place.³ So your body is actually dealing with an effective dose somewhat lower than the full 20 mg you ingested.

When Drug Interactions Could Change the Picture

The one scenario where a double dose might deserve a bit more attention is if you also take a medication that slows down how your liver processes montelukast. Because CYP2C8 handles the bulk of montelukast’s breakdown, drugs that block that enzyme can cause the drug to linger in your system much longer than usual.

The most studied example is gemfibrozil, a cholesterol-lowering drug. In a clinical pharmacokinetics study, gemfibrozil increased overall montelukast exposure in the body about fourfold and roughly doubled the time it took to clear.⁵ If you are on gemfibrozil or another CYP2C8 inhibitor and you accidentally double your montelukast, the effective drug exposure might be higher than in someone who is not taking those medications. This still does not make it dangerous per se, given the enormous safety margin, but it is worth mentioning to your pharmacist or doctor, especially if you notice anything unusual.

Interestingly, the common antifungal itraconazole, which strongly inhibits the CYP3A4 enzyme, had no meaningful effect on montelukast blood levels.⁵ This is a useful illustration: the enzyme your liver actually uses to break down montelukast is not the one older prescribing information emphasized. Product labels have historically listed CYP3A4 and CYP2C9 as the key enzymes, but research has since shown CYP2C8 is the real workhorse. If your pharmacist flags a CYP3A4 interaction with montelukast, the clinical reality is that it probably does not matter much.

A Double Dose versus an Ongoing Overdose

There is a meaningful difference between accidentally taking two pills once and chronically taking too much. The reassuring poison control data apply to single-event overdoses. If you have been accidentally taking double doses for days or weeks, for example because of a pharmacy mix-up or misunderstanding of your prescription, the situation is different enough to warrant a conversation with your doctor. Not because a crisis is imminent, but because sustained higher-than-normal blood levels over time could theoretically amplify side effects, particularly the ones montelukast is most watched for.

The Neuropsychiatric Side Effects Worth Knowing About

You may have heard about montelukast’s boxed warning related to mental health effects. The U.S. FDA added its most prominent warning label to montelukast in 2020, noting reports of agitation, depression, sleep disturbances, and suicidal thoughts in some patients. This warning applies to normal therapeutic doses, not specifically to overdose, but it is useful context when thinking about what a double dose means.

A systematic review of the evidence found that montelukast at regular doses was associated with a modestly higher risk of sleep problems, including insomnia.⁶ These are effects that develop over the course of ongoing treatment, not ones triggered by a single extra pill. If you have been taking montelukast for a while and already noticed mood changes or sleep disruption, it is worth discussing with your prescriber whether the drug is still the right choice for you. But the double-dose event itself is not going to create a sudden psychiatric emergency.

Animal research has explored the mechanism behind these neuropsychiatric effects. One study in rats found that high doses of montelukast caused decreases in brain chemicals involved in mood regulation, including dopamine, serotonin, and norepinephrine, in a pattern that worsened with dose.⁷ The doses used in that research were far above what any human would take even in an accidental double-dose scenario. The study is relevant to understanding the underlying science, not to predicting what happens when you take 20 mg instead of 10 mg.

Why Montelukast Is So Forgiving in Overdose

Montelukast works by blocking a specific receptor on cells called CysLT1. When the body’s inflammatory molecules (leukotrienes) try to bind to those receptors to trigger airway narrowing and allergy symptoms, montelukast sits in the way and prevents the effect. The drug works because at the normal dose, it already occupies a very high percentage of those receptors. Taking twice the dose does not meaningfully double the drug’s activity, because the receptors are already mostly blocked. The extra molecules simply circulate until your liver breaks them down and your body excretes the pieces.

This “ceiling effect” is a key reason why montelukast overdoses are so benign compared to, say, overdoses of drugs that directly affect heart rhythm or blood pressure. Once the target receptors are fully occupied, additional drug has nowhere useful to go and nothing dangerous to do.

When Children Take Extra Doses

Parents are often the ones who discover a double dose, either because a child grabbed the chewable tablet off a counter or because two caregivers each gave the evening dose without realizing the other already had. The data here are especially reassuring. The largest analysis of accidental pediatric montelukast exposures found that even among thousands of children who took amounts well above their prescribed dose, the vast majority experienced no adverse effects at all. Among the roughly 17,000 cases with known ingestion amounts, over 96 percent were managed entirely at home.²

The most common problem, when anything occurred at all, was a tummy ache. Moderate effects appeared in under half a percent of all cases, and serious effects in about two-tenths of a percent, even when the analysis included children who swallowed 50 mg or more.² If your child took a second chewable tablet, the practical advice is the same as for adults: skip the next dose, watch for stomach pain, and call Poison Control if you feel more comfortable hearing it from a professional.

Preventing Accidental Double Doses

This kind of mistake is incredibly common across all once-daily medications. You are in the middle of your evening routine, distracted by a phone call or a kid yelling from the other room, and you cannot remember whether you already took the pill. A few simple habits help:

Use a pill organizer: Weekly pill cases with compartments for each day make it immediately obvious whether today’s dose has been taken.
Set a phone alarm with a confirmation step: Rather than just an alarm that you dismiss, use a medication-tracking app that records the dose as taken when you tap “done.” Checking the log is far more reliable than checking your memory.
Keep the bottle in a consistent spot: If you always take it at the same time in the same place, the physical routine reinforces the memory. Moving between rooms before and after taking the pill creates a mental anchor.
Flip the bottle: Some people turn the medication bottle upside down after taking their dose, then right it again in the morning. A low-tech signal that works surprisingly well.

For households with children, storing montelukast chewable tablets up high and in a child-resistant container is standard advice. But the extra reassurance here is that even if a young child gets into the bottle, the safety profile means you have time to call Poison Control calmly rather than racing to the emergency room. About 80 percent of pediatric ingestion cases in the Texas poison control study were managed entirely on-site without any need for a hospital visit.¹

How Montelukast Compares to Other Common Medications in Overdose

Part of the reason people panic about a double dose is that we are trained to take medication overdose seriously, and rightfully so. Many common drugs can be genuinely dangerous in even moderate overdose. Acetaminophen, for instance, can cause life-threatening liver damage at doses only a few times above the recommended maximum. Certain blood pressure and heart medications can cause dangerously low blood pressure or slow heart rate with relatively small extra amounts.

Montelukast is not in the same category. Its mechanism of action, blocking a single inflammatory receptor, gives it very little ability to disrupt the cardiovascular, metabolic, or neurological systems in a way that would be acutely dangerous. This does not mean you should be careless with it, but it does mean that the appropriate emotional response to “I took two by accident” is mild annoyance, not fear. The evidence from tens of thousands of tracked cases supports treating this as a non-event for the vast majority of people.

1
Taylor & Francis Online (J Toxicol Environ Health A). Pediatric montelukast ingestions reported to Texas poison control centers, 2000-2005
2
PubMed Central. Adverse events are rare after single-dose montelukast exposures in children
3
PubMed. Pharmacokinetics, bioavailability, and safety of montelukast sodium (MK-0476) in healthy males and females
4
PubMed. Reevaluation of the microsomal metabolism of montelukast: major contribution by CYP2C8 at clinically relevant concentrations
5
PubMed Central. CYP2C8 but not CYP3A4 is important in the pharmacokinetics of montelukast
6
PubMed Central. Neuropsychiatric events associated with montelukast in patients with asthma: a systematic review
7
Al Mustansiriyah Journal of Pharmaceutical Sciences. High-Dose of oral Montelukast Induces Monoamines Depletion and brain-Derived Neurotrophic Factor BDNF Upregulation in male Rat’s Brain