underactive thyroid
"I have been taking Synthroid for about eight years now.  I have tried the generic Levoxothyrine and it makes shaky all over even at the same dosage.  My history has been going from hyperthyroid, caused by thyroiditis, to hypothyroid afterwards.  I take my dose religiously every morning 1 hour before breakfast.  Even in light of this I seem to have great fluctuations in my levels.  I assume this is more a physiological problem than that of the medication.  When we get it leveled out, I feel well."