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I occasionally get excercise induced asthma - normally it's to do with pollen and pollution
That sounds more like allergic asthma which you only notice if you're placing extra demands on your pulmonary system by exercising. True exercise induced asthma doesn't need anything else in the atmosphere to trigger it, just the exercise. IANAD, but allergic asthma probably responds better to a preventer (e.g. beclomethasone, brown inhaler) rather than a reliever (e.g. salbutamol, blue inhaler). With the steroidal preventer medication, it takes a period of routine administration (up to a week) to get the full benefit and it needs experimentation to dial in the dosing to suit the individual, there's at least a 10:1 range of dosing between individuals for the minimal dose which provides optimal benefit.
I occasionally get excercise induced asthma - normally it's to do with pollen and pollution. Nothing too awful, just short of breath and coughing after long hard rides, takes a few hours to die down. Did get an inhaler once (helpful doctor told me to stop riding, just in case) but it didn't do much to ease the symptoms, either taken prior or after. Can't remember what the drug was though.