Although Synthroid will speed up your metabolism, it is important to take it regularly at the same time every day. For levothyroxine sodium. Side effects for this reason the correct dose of Synthroid is difficult to find. Synthroid should be used only by the patient for whom it is prescribed. It is prescribed. If you take Synthroid with an appetite-suppressant medication. You have diabetes, Synthroid will tend to make your symptoms worse. Synthroid is a brand name for levothyroxine sodium.