An osmotic, floating gastroretentive composition comprising: a) a multilayer core comprising: (i) a pull layer comprising liothyronine or a pharmaceutically acceptable salt thereof, an acid, a gas-generating agent, a first osmogen, and at least one water-soluble hydrophilic polymer, and (ii) a push layer comprising a polyethylene oxide polymer with an average molecular weight of at least 900,000 Da, and a second osmogen; and b) a permeable elastic membrane comprising at least one orifice and covering at least a portion of the multilayer core; wherein the water-soluble hydrophilic polymer is selected from the group consisting of hypromellose, sodium carboxymethyl cellulose, and mixtures thereof; wherein the water-soluble polymer is present in an amount of from 5% w/w to 60% w/w, based on the total weight of the pull layer, wherein the first osmogen is present in an amount of from 5% w/w to 50% w/w, based on the total weight of the pull layer, wherein the second osmogen is present in an amount of from 5% w/w to 50% w/w, based on the total weight of the push layer, wherein the permeable elastic membrane comprises at least one copolymer of ethyl acrylate, methyl methacrylate and trimethylammonioethyl methacrylate chloride; and at least one plasticizer, wherein the at least one orifice is in fluid communication with the pull layer, and wherein the composition provides sustained release, while maintaining plasma concentration of from 0.5 ng/ml to 3 ng/ml, of liothyronine or a pharmaceutically acceptable salt, for at least 6 hours. a) a multilayer core comprising: (i) a pull layer comprising liothyronine or a pharmaceutically acceptable salt thereof, an acid, a gas-generating agent, a first osmogen, and at least one water-soluble hydrophilic polymer, and (ii) a push layer comprising a polyethylene oxide polymer with an average molecular weight of at least 900,000 Da, and a second osmogen; and (i) a pull layer comprising liothyronine or a pharmaceutically acceptable salt thereof, an acid, a gas-generating agent, a first osmogen, and at least one water-soluble hydrophilic polymer, and (ii) a push layer comprising a polyethylene oxide polymer with an average molecular weight of at least 900,000 Da, and a second osmogen; and b) a permeable elastic membrane comprising at least one orifice and covering at least a portion of the multilayer core; wherein the water-soluble hydrophilic polymer is selected from the group consisting of hypromellose, sodium carboxymethyl cellulose, and mixtures thereof; wherein the water-soluble polymer is present in an amount of from 5% w/w to 60% w/w, based on the total weight of the pull layer, wherein the first osmogen is present in an amount of from 5% w/w to 50% w/w, based on the total weight of the pull layer, wherein the second osmogen is present in an amount of from 5% w/w to 50% w/w, based on the total weight of the push layer, wherein the permeable elastic membrane comprises at least one copolymer of ethyl acrylate, methyl methacrylate and trimethylammonioethyl methacrylate chloride; and at least one plasticizer, wherein the at least one orifice is in fluid communication with the pull layer, and wherein the composition provides sustained release, while maintaining plasma concentration of from 0.5 ng/ml to 3 ng/ml, of liothyronine or a pharmaceutically acceptable salt, for at least 6 hours. wherein the water-soluble hydrophilic polymer is selected from the group consisting of hypromellose, sodium carboxymethyl cellulose, and mixtures thereof; wherein the water-soluble polymer is present in an amount of from 5% w/w to 60% w/w, based on the total weight of the pull layer, wherein the first osmogen is present in an amount of from 5% w/w to 50% w/w, based on the total weight of the pull layer, wherein the second osmogen is present in an amount of from 5% w/w to 50% w/w, based on the total weight of the push layer, wherein the permeable elastic membrane comprises at least one copolymer of ethyl acrylate, methyl methacrylate and trimethylammonioethyl methacrylate chloride; and at least one plasticizer, wherein the at least one orifice is in fluid communication with the pull layer, and wherein the composition provides sustained release, while maintaining plasma concentration of from 0.5 ng/ml to 3 ng/ml, of liothyronine or a pharmaceutically acceptable salt, for at least 6 hours.