CBD and Montelukast (e.g. Singulair, Montelukast-ratiopharm)

You are taking montelukast (e.g. Singulair, montelukast-ratiopharm) and wondering whether you can use CBD (cannabidiol) safely? This article provides a neutral overview of a possible CBD / montelukast interaction, explains the underlying mechanism, offers practical, cautious guidance, and highlights when to seek medical advice. You can jump directly to CBD and montelukast: What is known about the interaction?, the practical checklist or the frequently asked questions.

How does CBD work?

Cannabidiol (CBD) is one of over 100 cannabinoids found in the cannabis plant. It interacts with the endocannabinoid system (ECS), which is involved in regulating pain perception, sleep, mood and immune processes. CBD also affects various liver enzymes, including those of the CYP450 system, which are important for the metabolism of many prescription medicines. You can find more detail here: More about how CBD acts in the body.

How does montelukast work?

Montelukast is a leukotriene receptor antagonist used in the management of asthma and allergic rhinitis. It blocks the action of leukotrienes, which are associated with inflammation, narrowing of the airways and increased mucus production. Important: In addition to common side effects, neuropsychiatric symptoms have been reported (e.g. agitation, sleep disturbances, low mood, suicidal thoughts). These risks are highlighted in official information (FDA Boxed Warning, 2020).

CBD and montelukast: What is known about the interaction?

Interaction mechanism: CBD, montelukast and liver enzymes (CYP2C8, CYP3A4, CYP2C9)

Montelukast is broken down mainly via the liver enzyme CYP2C8, and to a lesser extent via CYP2C9 and CYP3A4. Primary data confirm the key role of CYP2C8 in montelukast metabolism.

CBD can inhibit several of these enzymes – particularly CYP3A4 and CYP2C9, and in vitro also CYP2C8. Inhibition of UGT enzymes (e.g. UGT1A9, UGT2B7) has also been described.

The possible consequence of combining CBD and montelukast is a slower breakdown of montelukast, which could lead to higher drug levels and, in turn, an increased likelihood of side effects (for example, headache, unusual dreams or mood changes).

Evidence base for the CBD–montelukast interaction

The in vitro inhibitory effects of CBD on CYP and UGT enzymes are relatively well described. However, clinical data specifically on the combination of cannabidiol and montelukast are largely lacking, so the interaction remains theoretical.

For context: strong CYP2C8 inhibitors such as gemfibrozil have been shown to increase montelukast exposure significantly (this direction of interaction is documented in product and regulatory information). CBD is considered a weaker inhibitor by comparison, but the direction of a possible CBD drug interaction with montelukast could be similar (increased montelukast levels).

Because montelukast is associated with important neuropsychiatric warnings, and CBD can influence liver enzymes, caution is advisable, particularly in more vulnerable groups (children and adolescents, people with liver disease, those taking multiple medicines, people with a psychiatric history, pregnant or breastfeeding individuals).

Use our interactive tool to explore possible CBD drug interactions with medicines:

Practice: How to reduce potential risk with CBD and montelukast

The following checklist summarises practical, non-alarmist steps if you are considering CBD while taking montelukast. It does not replace personalised medical advice.

Before starting CBD alongside montelukast

• Prepare an up-to-date list of all medicines (including over-the-counter products, alcohol use and supplements).
• Discuss any pre-existing conditions, especially liver disease, and recent liver function tests with your doctor.
• Clarify your goal for CBD use (e.g. sleep, general wellbeing) and set realistic expectations.
• Exercise particular caution in children/adolescents, people with liver disease, those taking multiple medicines, people with a psychiatric history, and during pregnancy or breastfeeding.

During use: dosing, timing and monitoring

• Start with a low CBD dose and increase slowly (“start low, go slow”).
• Where medically appropriate, consider a time gap of around 2–3 hours between taking CBD and montelukast. Try to avoid taking both at exactly the same time.
• Keep a simple symptom diary (date, dose, time of intake, new or changed symptoms such as unusual dreams, mood changes, sleep quality, headaches, abdominal pain).
• Ask your doctor whether more frequent liver function tests are advisable, especially if using higher CBD doses or other medicines that affect the liver.

Warning signs – when to seek medical advice

• New or worsening neuropsychiatric symptoms: agitation, anxiety, low mood, aggression, sleep disturbances, nightmares, suicidal thoughts.
• Possible signs of increased montelukast exposure: more intense or more frequent headaches, abdominal pain, dizziness, unusual dreams, noticeable mood swings.
• Possible signs of liver involvement while using CBD: marked tiredness, persistent nausea, dark urine, yellowing of the skin or eyes.

Practice example (fictional): An adult with seasonal rhinitis takes 10 mg montelukast in the evening. They would like to try CBD oil for sleep difficulties. A possible approach: clarify the plan with a doctor beforehand, use a very low initial CBD dose, take CBD in the early evening and montelukast as usual later (about 2–3 hours apart). Then observe for 1–2 weeks, keep a diary, and seek medical advice immediately if any new psychological symptoms occur.

Overview of side effects of CBD and montelukast

CBD side effects and metabolism

Commonly reported side effects of CBD include tiredness, diarrhoea, dry mouth and changes in appetite. In higher doses, raised liver enzymes have been observed in some studies.

CBD can inhibit enzymes that help to break down medicines, particularly within the CYP450 system (for example CYP3A4, CYP2C9 and in vitro CYP2C8). Because of this, CBD metabolism and its impact on liver enzymes can be relevant when it is combined with other prescription medicines such as montelukast.

Discuss any CBD use with a healthcare professional – especially if you are taking medicines regularly or have a liver condition.

Montelukast side effects (including neuropsychiatric information)

Common side effects of montelukast include headache, abdominal pain, dizziness or cough.

Important: In rare cases, behavioural and mood-related symptoms have been reported (e.g. agitation, sleep disturbances, nightmares, low mood, suicidal thoughts). These risks are highlighted in official medicine information (FDA boxed warning). If you notice new psychological symptoms, seek medical advice immediately.

CBD and montelukast: comparison overview

Disclaimer: This article is for information purposes only and does not replace medical advice. Do not change medicines or dosages without consulting your doctor. No claims are made regarding the treatment or cure of illnesses.