If you increase your running gradually, then asthma should really not be a problem. I have pretty bad asthma, and I played lacrosse, which, if you didn't know already, involves an ungodly amount of running. Now, when I played,the trick was to remember to pace yourself. You can't run at full speed because not only does it tire you out and exhaust you quicker, you also are more prone to asthma attacks because you run out of breath and wheezing and pain/uncomfortablilty becomes the problem. So when you run, do a slower warm up kind of run, maybe 5-8 minutes, and then you can work yourself up to a faster pace. Also, you need to keep hydrated. When you run a lot, and begin to increase breathing rate, your mouth and throat are going to get dry; bad, bad thing for someone with asthma. Water and whatnot should keep you refreshed and help out with asthma worries, trust me on that. A last thing to remember is that you should not just flat out stop running. When you are near finishing, it's best to do a cool-down run and gradually slow down to a walk. It's never good to just run and stop, period. This kind of thing allows for you to let your body adjust to the changes. And if you take any prevention medicine, go ahead and take that a little before you run, just to be safe. Just keep building yourself up, and the longer you keep at it like that, the better you'll be able to run without asthma having an effect on your running. Just remember if you stop, it is really hard to work yourself back into that condition. I haven't ran for almost a year now, because I'm not doing lacrosse this season, and now I have difficulty running in small distances without feeling like asthma is taking some toll on me.

short and simple. take a puff of your inhaler before you run because if you run and become out of breath it is too late to fully calm it down. Control your asthma also.