This study is about the guidelines of World Health Organization for stability testing of pharmaceutical products containing well established drug substances in conventional dosage forms. For these pharmaceutical products the stability studies may be restricted to dosage forms because for established drug substances, literature data is available on the decomposition process and degradability of the active substances along with adequate analytical methods. Thus the actual stability of these dosage forms depends on the formulation and packaging-closure system selected by the manufacturer so the stability considerations, e.g. selection of excipients, determination of their level and process development, should be given high priority in the developmental stage of the product. With the approval of the drug regulatory authority, a tentative (provisional) shelf-life is often established, provided that the manufacturer has undertaken, by virtue of a signed statement, to continue and complete the required studies and to submit the results to the registration authority