How are the medicines we take on a daily basis absorbed and excreted? Why does it take a certain amount of time for a drug to start working? Why must we take them again at certain intervals? Except for drugs that promote digestion and regulate gastrointestinal function, which work directly in the stomach or intestines, most drugs are absorbed mainly in the small intestine and reach the whole body through the bloodstream, and the blood concentration rises to a certain level and starts to take effect. At the same time, our body has to work to dispose of foreign substances like drugs as early as possible and to excrete them from the body. It is the liver and kidneys that take on this task. The drug in the blood is metabolized in the liver, and the blood level decreases over time. When the blood is filtered through the kidneys, the metabolites of the drug are removed from the blood and sent to the bladder, where they are excreted with the urine. For a drug to work, the blood concentration must be kept above a certain level. For example, antibiotics lose their antibacterial effect when the amount of the drug in the blood falls below a certain level, and bacteria begin to multiply. Therefore, it is important to take the drug again before the blood concentration decreases to the minimum effective concentration. Take the medication as prescribed to keep the blood concentration within the appropriate range for a long time in order to make the medication effective. However, if you take the amount twice together at the next dose because you forgot to take the drug on a certain occasion, it can lead to an excessive blood concentration and unexpected side effects. It is important to take the medication correctly according to the prescribed usage and dosage.