Microdosing, or micro-dosing, is a technique for studying the behaviour of drugs in humans through the administration of doses so low (“sub-therapeutic”) they are unlikely to produce whole-body effects, but high enough to allow the cellular response to be studied. This is called a “Phase 0 study” and is usually conducted before clinical Phase I to predict whether a drug is viable for the next phase of testing. Human microdosing aims to reduce the resources spent on non-viable drugs and the amount of testing done on animals.
Less commonly, the term “microdosing” is also sometimes used to refer to precise dispensing of small amounts of a drug substance (e.g., a powder API) for a drug product (e.g., a capsule), and when the drug substance also happens to be liquid this can potentially overlap what is termed microdispensing. Wikipedia