Synthro is is a compound used in the treatment of hypothyroidism. Its major function in the body is to aid in the metabolism of fat into protein. In bodybuilding circles Synthroid is used before contests to give the user an extra lean look. It also has the added bonus of giving users some extra energy from the calories burned in the fat.
Synthroid has been found to work especially well with HGH and has seen a bit of resurgence in popularity as HGH becomes more widely used in bodybuilding and athletic circles.