A solid dispersion comprising suvorexant or a salt thereof in amorphous form and at least one pharmaceutically acceptable matrix compound wherein the matrix compound is (i) a polymer and wherein the solid dispersion contains the suvorexant or salt thereof in an 5 amount of at least 50 weight % based on the combined weight of the suvorexant or salt thereof and the at least one matrix compound or (ii) a silicon based inorganic adsorbent.