With regular use, tolerance to and dependence on drugs can develop. Withdrawal symptoms may also be experienced if the drug is reduced or stopped.

Tolerance: A person needs more of a drug in order to achieve the same effects they felt previously with smaller amounts.

Dependence: Use of the drug becomes central to a person's life, and they may experience withdrawal symptoms if they stop using the drug.

Withdrawal: Describes a series of symptoms that may appear when a drug on which a user is physically dependent is stopped or significantly reduced. The withdrawal symptoms vary depending on a range of factors including the drug type and tend to be opposite to the effects produced by the drug. The body is always trying to maintain a state of balance. When the body has become accustomed to the drug for normal function and use is ceased, the body will try to counterbalance for the change producing withdrawal symptoms.