METHODS: An in vitro testing apparatus was set up using industry standard inhaler testing devices. Inhalers were actuated during simulated inhalation and particles which traveled through the throat model and reached a downstream filter were measured as the in vitro lung deposition. Metered dose inhalers (MDIs) and dry powder inhalers (DPIs) were tested at varying altitudes from 670m to 4300m. MDIs were also tested at a range of temperature conditions including inhaler and ambient temperatures of -10°C, 0°C, 10°C, 20°C and 40°C. The inhaler and ambient temperatures were varied separately in order to simulate real patient conditions.