I have been on Levoxyl for 4 months now. Started at 100 mcg and then to 125 mcg and have just had my dosage of Levoxyl increased to 150 mcg and I have been experiencing a heartburn like tighness in my chest since the day after the increase to 150 mcg. I was wondering if anyone else has experienced this side effect. I felt fine at 125 mcg but my T4 levels were still way below normal. Does any one have any insight?