I haven't been diagnosed with Hashimoto's, but I probably have it since my mother was diagnosed with it and I've was diagnosed with an underactive thyroid when I was 17. When I first started trying to figure out was wrong, the first thing the doctor did was put me on synthroid (right now I'm at 75 MCG, but based on the way I've been feeling, I think the dosage will probably go up when I go back to the doctor's next month).For me, the synthroid only alleviates constipation for the first week the dosage is changed; by the end of the week, I'm back to the way I was before, so I don't really know to what extent my constipation relates to my thyroid.Also, when I was first looking for a diagnosis, I found research suggesting that IBS, hypothyroidism, endometriosis, and autoimmune disorders were all correlated; having one makes it more likely that you have another.