Disclosed is a drug delivery system for administration of a pharmaceutically active substance that is a cationic amphiphile by itself and has a solubility per se in water of at least 4 mg/ml, wherein the drug delivery system comprises nanoparticles smaller than about 50 nm having a solubility in water below 0.1 mg/ml, said nanoparticles being formed by said substance in association with a sodium salt of the methyl ester of N-all-trans-retinoyl cysteic acid, a sodium salt of methyl ester of N-13-cis-retinoyl cysteic acid, or a combination thereof. Also disclosed is a composition comprising the delivery system and the method of preparing a drug delivery system or a composition comprising the delivery system and the use of the drug delivery system or a composition comprising the delivery system in the manufacture of a medicament. Further disclosed is the use of a sodium salt of the methyl ester of N-all-trans-retinoyl cysteic acid, a sodium salt of the methyl ester of N-13-cis-retinoyl cysteic acid, or a combination thereof in the preparation of a drug delivery system and a method for enhancing drug efficiency or bioavailability.
