I am so lean. how could i build my body accurately.? is der any medication or tonic to become bit fat?

If healthy, protein: If you are feeling well, and ideally have been evaluated by a physician recently to be sure you do not have a metabolic condition (such as thyroid disease or diabetes) and are not taking stimulant medications, then adding a protein supplement to your regular diet--without reducing your usual intake--can help. This can be as a snack bar, meal-replacement bar, or powder you add to drinks.