Is it dangerous to go under aenesthesic for a surgery while on synthroid (thyroxine)? i read the drug combination may cause arrythmia.

No: Be sure to let your doctors know that you are taking synthroid, (thyroxine) but there should be no need to worry.

Should be ok!: We often operate on people who are on thyroid replacement. The important piece is that your thyroid hormone levels should be appropriate. You just have to be careful that you are not under or overdosing your body on thyroid hormone.