Bioavailability refers to the extent and rate at which the active moiety (drug or metabolite) enters the systemic circulation, thereby accessing the site of action. Bioavailability (F) describes the fraction of a dose of drug that reaches the systemic circulation. Bioavailability of a single drug may vary significantly depending on the route of administration. In pharmacology, bioavailability is a subcategory of absorption and is the fraction (%) of an administered drug that reaches the systemic circulation. [1] The bioavailability of the active pharmaceutical ingredients (API) corresponds to the dose entering the bloodstream and consequently, its effectiveness [2]. For this reason, a drug’s bioavailability must be considered when designing a therapy and dosage. Bioavailability is the percentage of a drug that actually reaches your bloodstream and becomes available to work in your body. When you swallow a pill, not all of it makes it into circulation. When a substance such as a medicine or supplement enters your system, the portion of the total substance introduces which can effectively create a response determines that substance’s bioavailability. The bioavailability of a substance can fluctuate, depending on the route of administration. Bioavailability is the amount of a nutrient in your food that actually gets absorbed and used by your body. It’s not the same as the total amount listed on a nutrition label.