Methacholine
Methacholine is a diagnostic agent used in challenge testing to assess airway hyperresponsiveness and help diagnose asthma and related respiratory conditions. When inhaled, it causes bronchoconstriction by stimulating muscarinic receptors in the airways. This test is performed under controlled clinical conditions to measure how sensitive a patient's airways are to cholinergic stimulation.
Methacholine is used in diagnostic testing to help diagnose asthma by measuring airway sensitivity to a bronchoconstricting agent.
This medication carries a boxed (black box) warning — the strongest type of FDA warning. Review the full prescribing information before use.
Key facts at a glance
- ATC
- V04CX03
- RxNorm
- 155080
- Generic
- Methacholine
- Class
- atc-v04
- Brands
- —
- Availability
- rx
- Lactation
- unknown
- Routes
- topical, ophthalmic
- Forms
- ointment, solution
- Regions
- US, EU, CN, JP
- Monitoring
- —
This page is for informational purposes only.
Do not use this information to diagnose yourself or to replace a physician's advice. Always consult a qualified healthcare provider before starting, stopping, or changing any medication. If you believe you are experiencing a medical emergency, call your local emergency number immediately.
Methacholine challenge testing is primarily used to diagnose asthma in patients with suspected but unconfirmed disease, evaluate airway hyperresponsiveness, and assess respiratory symptoms that may be asthma-related. It is also used to rule out asthma when other diagnostic tests are inconclusive.
Methacholine chloride is a synthetic cholinergic agonist that binds to muscarinic receptors on bronchial smooth muscle. This activation triggers bronchoconstriction through parasympathetic nervous system stimulation. In patients with hyperreactive airways (such as those with asthma), even small doses will cause significant airway narrowing, which is measured to determine the degree of hyperresponsiveness.
Methacholine should only be administered in a controlled clinical setting with appropriate emergency equipment (including bronchodilators) readily available, as it can cause significant bronchoconstriction. The test is contraindicated in patients with severe asthma, active respiratory infection, or recent myocardial infarction. Results should be interpreted by qualified healthcare professionals familiar with the test protocol.
Official drug label
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This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.
This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.
If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.
Medically reviewed by WellAlly Editorial Team Last reviewed July 26, 2026. · Read our editorial policy