How Medications Get Absorbed By Your Body

Medication absorption refers to how a drug moves from its administration site into the bloodstream. Oral drugs dissolve in the stomach or pass to the small intestine, the main absorption site, where they enter the portal venous system to the liver for the first pass effect. This can inactivate part of the drug before it reaches general circulation. Unlike oral drugs, intravenous (IV) drugs enter the bloodstream directly, bypassing the GI tract, while intramuscular and subcutaneous injections also avoid GI absorption. Bioavailability is the degree a drug is absorbed into the bloodstream, with oral drugs typically having less than 100% bioavailability due to the liver's first pass effect, while IV drugs have 100%. Different drug formulations affect absorption rates, with factors like dissolution rate, surface area, blood flow, lipid solubility, and pH differences influencing the absorption process. Faster dissolving drugs are absorbed quicker, and the greater surface area of the small intestine enhances absorption compared to the stomach.