Provocholine® (methacholine chloride) is indicated in adults (aged 17 and over) to detect bronchial airway hyperreactivity, to assist in the diagnosis of asthma when the clinical history is suggestive of the condition but there is normal spirometry and the diagnosis remains uncertain after additional evaluation. Provocholine® is a bronchoconstrictor agent for diagnostic purposes only and is to be administered by inhalation. The testing should be conducted under specialist medical supervision by a doctor familiar with all aspects of the methacholine challenge test, all contraindications, warnings and precautions. The patient must never be left unattended during the test. Emergency equipment and medication must be available immediately to treat acute respiratory failure. Laboratory staff with asthma or allergies should be particularly careful and take necessary measures when performing the test on patients. As a result of the administration of Provocholine®, severe bronchoconstriction and a reduction in respiratory function may occur. If severe bronchoconstriction occurs, this must be immediately reversed by administration of a rapid-acting inhaled bronchodilator agent (beta-agonist), precautions for which must be taken when the inhalation challenge test is performed in patients receiving beta-blockers since it is possible that bronchoconstriction may not be reversed easily. Contraindications include hypersensitivity to the active substance or other parasympathomimetic agents or abnormal baseline spirometry (FEV1/ FVC ratio less than 70%). Adverse reactions associated with inhaled methacholine challenge tests are rare, and include incidences of headache, throat irritation, light-headedness and itching.