Food is the number one addictive substance. Followed by illegal drugs which have controls on them by a government and are illegal in certain situations (a person is not allowed to have them). A drug is any chemical designed to affect the human body. A psychoactive drug is a drug that affects the brain. Some controlled drugs are allowed if you have permission (called a “prescription”) from a doctor. Other drugs are illegal – meaning you are never allowed to have them. Alcohol, caffeine (coffee), nicotine (tobacco), aspirin and acetaminophen/paracetamol (Tylenol) are all drugs.