Some drugs affect the way you think, feel and act , and may sometimes cause people to be sad, silly and even mean. Some drugs like tobacco and marijuana make it hard for people to breathe properly and can also cause lung cancer. Drugs like alcohol can stop the liver from working properly and can cause liver disease. The intestines help you digest food. Drug use can affect this process and may cause nausea, diarrhea, or make you throw up.
Some drugs can upset the stomach lining and cause ulcers and cancer.
Some drugs speed up your heart rate while others slow it dowm.