Triiodothyronine treatment for Raynaud's phenomenon: a controlled trial. The effects of 80 micrograms triiodothyronine (T3) daily were compared with placebo in a double blind controlled crossover trial in 18 patients with Raynaud's phenomenon. Reductions in the frequency, duration and severity of attacks while taking T3 were gradual but highly significant. Four of 6 subjects had skin ulcer healing. Skin temperatures in the hands increased significantly. The skin temperature recovery times after cold exposure were significantly shorter during T3 therapy compared with placebo. Although large dosages of T3 were well tolerated, 6 patients experienced episodic palpitations, and slight but significant increases in heart rate and pulse pressure were observed. Evaluation of the use of physiological doses of T3 (60 micrograms daily or less) in the treatment of Raynaud's phenomenon is suggested. 