Evaluate single dose (2 x 2.5mcg/puff; total dose 5mcg) effect of tiotropium administered 30 minutes prior to allergen challenge on allergen-induced EAR assessed as the maximal % fall in FEV1 after allergen inhalation compared to that of single dose (two puffs) matched placebo administered 30 minutes prior to allergen challenge.

Inclusion Criteria:

• age (years) at least 18 years
• no confounding health issue (i.e. no health conditions, other than asthma, that would put the participant at risk or affect data integrity as determined by the principal investigator)
• baseline FEV1 ≥ 65% of predicted normal at Visit 1
• evidence of atopy to an allergen suitable for inhalation challenge following skin prick testing such as house dust mite, grass, cat or horse
• fall in FEV1 of ≥ 20% at a dose of methacholine ≤ 600mcg (methacholine PD20) at Visit 1
• positive response to allergen inhalation challenge (fall in FEV1 of ≥ 15% after inhalation of allergen at a dilution 1:32 or more dillute.
• absence of respiratory infection for at least 4 weeks prior to Visit 1
• absence of significant worsening of asthma that requires health care intervention or prolonged change in medication due to allergen exposure (or other trigger) for at least 4 weeks prior to Visit 1
• women of child-bearing potential shall not be pregnant or lactating
• non-smoker (cigarettes, vaping); ex-smoker with <10 pack year history allowed; cannabis use will be evaluated on a case-by-case basis
• if on as needed budesonide/formoterol therapy, no reported use within 3 weeks prior to allergen challenge

Exclusion Criteria:

• Smoker >10 pack year history