The invention provides the use of compounds of formula (I) or pharmaceutically acceptable esters, amides, solvates or salts thereof, including salts of such esters or amides, and solvates of such esters, amides or salts, for the manufacture of a medicament for the treatment or prophylaxis of a condition that may be treated with a thyroid receptor agonist or partial agonist wherein R.sup.1, R.sup.2, R.sup.3, R.sup.4, Y, W and R.sup.5 are as defined in the specification. The invention also provides compounds of formula (Ia) or pharmaceutically acceptable esters, amides, solvates or salts thereof, including salts of such esters or amides, and solvates of such esters, amides or salts, formula (Ia) wherein R.sup.1, R.sup.2, R.sup.3, R.sup.4, Y, W and R.sup.5 are as defined in the specification. ##STR00001##