To those of you who take medication regularly: If you get side effects from the medication, what factors lead to you continuing to take the medication?

I recently started on Imitrex for migraines, and it makes the migraine go away quickly, but it makes my muscles tense up, which makes me very, very tired. But I don't have a migraine, so I continue to take Imitrex because being able to function at work while tired is easier for me than functioning with a migraine.

Anyone else make these kinds of determinations?