Inclusion Criteria:  diagnosis of asthma asthma is currently well controlled using only occasional bronchodilators baseline lung function (FEV1) is greater than 65% of the predicted value exhibit bronchoconstriction to inhaled methacholine at a dose of 200mcg or less  Exclusion Criteria:  women who are pregnant or breastfeeding. diagnosis of another lung condition or medical condition that would pose a risk to the participant if enrolled in the study current smokers of nicotine products (e.g., cigarettes). users of cannabis or other inhaled recreational products (e.g., e-cigarettes or other vaping products) on a daily basis respiratory infection within 4 weeks of entering the study use of any anticholinergic agent within 30 days prior to the beginning of the study (e.g., ipratropium or the study treatment tiotropium). known hypersensitivity to tiotropium bromide or components of tiotropium formulation (e.g., benzalkonium chloride), to atropine or its derivatives.