The brain controls many parts of our body, yet even though its is very complex it can be effected badly in many ways. The main things that can affect the brain would be Alcohol and drugs. Alcohol is a type of depressant that slows down the brain in terms of processing info. Drugs on the other hand just have physiological changes in general, so overdose is bad. Affects caused by drugs and alcohol can consist of horrible judgement,impaired senses, addiction, and change in the brain chemistry.
Drugs affect the brain in many ways in negative manners. One way is that when you abuse cocaine it messes up your dopamine receptors and could trigger memory loss and decreased learning capability. Cocaine itself is used to make people feel pleasure but too much can cause problems in regular day events. This is also known to people as Methamphetamine abuse. Other known symptoms of drugs are paranoia, hallucinations and even sometimes depression.