The present invention relates to the use of uncrosslinked copolymers having a backbone comprising i) a plurality of thermo-responsive structural units derived from one or more than one N-alkyl or N,N-dialkyl substituted (alkyl)acrylamide monomer and ii) a plurality of hydrophilic structural units derived from one or more than one second ethylenically unsaturated monomer as excipients in solid mixtures with poorly water-soluble substances for effective solubilization of the latter in aqueous media. Solid dosage forms comprising a solid mixture of such copolymer(s) and poorly water-soluble substance(s) are also within the scope of the invention.