In the treatment of hypothyroidism, thyroxine is preferred over liothyronine because of thyroxine:: (A) Is faster acting, (B) Has higher affinity for thyroid hormone receptors, (C) Has a longer half life, (D) Can be made more easily by recombinant DNA technology
Answer is C. Liothyronine (T3) as compared to thyroxine (T4) is:

Fast acting
More potent
Short half-life

An indication of liothyronine includes myxedema coma and for most of the indications, thyroxine is used because it has a long half-life thus can be used less frequently than T3.