Addictions start with voluntarily trying a substance, but soon the body becomes dependent on it. This physical dependence is the first mark of an issue with substance abuse. A growing tolerance to the substance as well as withdrawal symptoms start to occur, so you will need more of the substance to get the same effects you are used to. Withdrawal symptoms can occur within hours of your last dose of a substance – your body’s signal that it is dependent. Symptoms can be severe and can result in seizures or even death.