Sustained release dosage forms are designed to rele ase a drug at a predetermined rate by maintaining a constant drug level for a specific pe riod of time with minimum side effects. In the recent years, focus on the development of controlle d release drug delivery systems has increased. The basic rationale of controlled release drug deli very system optimises the biopharmaceutical, pharmacokinetic, and pharmacodynamic properties of a drug in such a way that its utility is maximized, side-effects are reduced and cure or con trol of the condition is achieved, in the shortest possible time by using smallest quantity o f drug administered by the most suitable route. There are several advantages of sustained release d rug delivery over conventional dosage forms like improved patient compliance due to less freque nt drug administration, reduction of fluctuation in steady-state drug levels, maximum ut ilisation of the drug, increased safety margin of potent drug, reduction in healthcare costs throu gh improved therapy, shorter treatment period and less frequency of dosing. SR products are desig ned to bring the blood level of a drug immediately to therapeutic concentrations by means of an initial dose portion and then sustain this level for a certain predetermined time with th e maintenance portion .SR of drugs in gastro- intestinal tract following oral administration is n ot affected by the absorption process. SR oral dosage forms have become more important in therapy as a means of reduced dosing frequency, hence potentially improving patient compliance and consequently efficacy. The principal goal of SR dosage forms is the improvement of drug therapy assessed by the relationship between advantages and disadvantages of the use of SR syste ms.