This book reveals the important key point for development of formulation and to ?nd out circadian rhythm i.e. suitable indicator, which will trigger the release of drug from the device. The primary readers of this book are UG and PG students enrolled in medical, Nursing and pharmaceutical science. This book will help them to understand the important consideration to be kept in mind before the development and delivery of dosage form when the risk or intensity of the symptoms of disease vary with time as in the case of allergic rhinitis, arthritis, asthma, myocardial infarction, congestive heart failure, stroke and peptic ulcer disease. The secondary reader for this textbook is research and development personal particularly those working in pharmaceutics, biopharmaceutics and pharmacokinetics. We acknowledge Department of Science and Technology (No.SR/FST/LSI-434/2010), New Delhi (SERC Division), India under DST -FIST scheme as well as the Maulana Azad National Fellowship (MANF) UGC, New Delhi, India for providing financial assistance