I have to stop taking synthroid (thyroxine) for a thryroid scan test. what are the side effects, i have been on medication for 8 years?

Mild if any symptoms: Synthroid (thyroxine) replaces hormone normally made by your thyroid. It helps maintain body heat, metabolism, energy. Stopping medicine for a a few days may make you mildly fatigued, a bit sensitive to cold, and less hungry, but should not cause serious symptoms. Some people don't even notice the difference especially in warm weather.

Fatigue: Main symptom would likely be fatigue. May get constipated, palpitations, restless feelings, being grumpy. But if u'r doc ordered I strongly suggest u follow up. It's only a week, and u may not even experience much.