A modified release composition comprising tacrolimus releases less than 20% w/w of the active ingredient within 0.5 hours when subjected to an in vitro dissolution test using USP Paddle method and using 0.1 N HCl as dissolution medium and has increased bioavailability by effectively reducing or even avoiding the effects of CYP3A4 metabolism. The modified composition may be coated with an enteric coating; and/or may comprise a solid dispersion or a solid solution of tacrolimus in a hydrophilic or water-miscible vehicle and one or more modifying release agents; and/or may comprise a solid dispersion or a solid solution of tacrolimus in an amphiphilic or hydrophobic vehicle and optionally one or more modifying release agents.