The present invention relates to dosage forms comprising a compressed blend of a biologically active ingredient, one or more polymers like a poly(a-hydroxy carboxylic acid) in which optionally is incorporated a glass transition modifying agent, and optional further ingredients, wherein the polymer or polymeric mixture has a specific glass transition temperature which causes the system to be in the glassy state at ambient conditions before administration and to be in the rubbery state under the physiological conditions to which the system is exposed after administration, resulting in pulsed release of said biologically active ingredient.
