This book includes certain important aspects related to a drug and the optimization of its formulation. The studied drug , i.e. Bupropion Hydrochloride is having potential to act against the depression of youngsters (Major Depressive Disorder) and also helps in cessation of smoking. So, for the enhancement of activity of drug inside the body, a desirable sustained release formulation is prepared which is able to release maximum amount of drug within 12 hrs. This will enhance the patient compliance, as people undergoing with the depression will obtain the drug with sustain release without the repetition of dosing of Bupropion. So, to prepare an optimized formulation of drug, one of the relevant technique of Design of Experiment (DoE) is utilized which is Formulation by Design (FbD). This techniques helped to design the best formulation by taking optimum concentration of chosen dependent and independent variables.