I wondered about this a few weeks back, too, but my mesalamine is Asacol. I definitely think that there is a relationship between hair loss and mesalamine, and maybe yours was triggered by the change in your meds.
But, I also think there are probably other factors involved, like lack of protein, hormone shifts (as quincy mentioned, thyroid, for example), and other nutritional changes that occur when you switch meds. There are so many factors that could apply.
My best reassurance was from my hair dresser, who told me that I had no bald patches and tons of little hairs growing back in. They're also growing in thicker and curlier. What a relief! You might check with your hairdresser.