Most commonly, depot injections are designed to have a duration of 2–4 weeks of action,[6] however the pharmacokinetics of a specific formulation vary. Absorption and metabolism can both be affected by modifying the drug itself (for example, by attaching a functional group) or by the formulation of the product (examples are oil or microsphere preparations).[6] Repeated administration of depot injections can lead to a half life over one month (as in some preparations of fluphenazine), but this can be variable in different patients.[7]