Drugs may be used to treat disease, reduce the sensation of pain, or help calm us down. In addition, they may change our mood by affecting the brain. Depressants have a relaxing effect because they depress the central nervous system. In high doses they can lead to sleep or act as an unaesthetic, causing unconsciousness. You need to be able to describe the effects of alcohol and heroin, the dangers of their misuse and the personal and social problems they can cause.
Tobacco smoke contains a large number of toxic chemicals. The main ones are carbon monoxide, nicotine, smoke particles and tar. Note that these chemicals can affect other parts of the body as well as the respiratory system.