Are there risks associated with taking imitrex (sumatriptan) for migraines on a long term basis, for 1-2 migraines per month?

None that we know of: So long as the long term usage remains at 1-2x/month. If at some point the patient or doctor recognizes that things are escalating to 2-3/month or 3-4/month...even though these are still below what would be considered CHRONIC patterns of dependency it should be clear that something is changing that needs to be dealt with...otherwise, long term use @ 1-2x/month is fine. BTW, you should start DIARY