Controlled Release, Sustained release, prolonged release, modified release ,extended release or depot formulations are used to identify drug delivery systems that are designed to achieve or extend therapeutic effect by continuously releasing medication over an extended period of time after administration of a single dose.There are several reasons for attractiveness of these dosage forms: provides increased bio-availability of drug product, reduction in the frequency of administration to prolong duration of effective blood levels, reduces the fluctuation of peak trough concentration and side effects and possibly improves the specific distribution of the drug. Controlled Drug Delivery Systems needs safe and effective controlled release polymers.