Different drugs affect the body in different ways, but all drugs chemically alter the brain. The drug effects that occur in individuals who consume drugs depend on how the brain processes the chemicals in each drug. The amount of drugs needed to cause certain effects vary as well. All of an individual's perceptions are controlled by the brain; therefore, the brain dictates the effects of drugs in individuals. What a person feels, hears, smells, tastes, thinks, and sees depends on what the brain is communicating to the individual's body. The brain and body have normal functioning patterns and operate according to very specific patterns when a person does not consume substances that cause any type of chemical disruption. However, when chemicals are introduced to the brain, the chemical messengers in the brain are altered, causing the brain to send a different set of signals to the body. Chemicals can cause individuals to see, think, and act very differently than they normally would, which is why drug abuse affects individuals and the world around them.