The invention relates to an implantable active ingredient depot for therapeutically active substances. The fields of application are in medicine and the pharmaceutical industry. The implantable active ingredient depot is constituted of a lipid matrix capable of forming cubic phases into which modifier molecules have been integrated and contains pharmaceutically active substances. A preferred lipid matrix is monooleine. The implantable depot of the invention is useful for the treatment of tumors in oncological therapy and in gene therapy. A rational membrane design allows control of the release of the active ingredients over time and also control of the amount released.