What medicines affect our body is known as pharmacokinetics. After a drug has been absorbed in the body and the drug is in the blood stream, medicine begin to work on different parts of the body.
Medicine can increase or decrease the level of hormones, it can make cells more or less sensitive to hormones in the body, medicine can destroy abnormal cells, replace deficient substance in the body. Some drugs fight infections. Some antibacteria stop the growth of bacteria (bacterostatic) while others kill the bacteria (bacterocidal).