Long-term use also changes other chemical systems and circuits in the brain, which can affect learning, judgement, decision-making, stress, memory, and behaviour. Because of how addiction works, many people who use drugs keep doing it even though they know the bad things that could happen if they keep doing it.
Why do some people get used to drugs while others don't? There is no single sign that a person will become dependent on drugs. Several different things affect how likely it is that someone will become addicted. The more risk factors a person has, the more likely it is that using drugs will cause them to become addicted to those drugs.
Biology. About half of a person's likelihood of becoming addicted is based on the genes they get from their parents. Other things that may make drug abuse and addiction more likely are a person's gender, race, and the presence of other mental problems.
Environment. There are many different things that make up a person's environment, such as their family, friends, economic situation, and overall quality of life. Peer pressure, physical and sexual abuse, early exposure to drugs, stress, and parental supervision can all make it more likely for someone to start using drugs and become addicted to them.