Substance addiction is the uncontrolled dependency on an addictive and harmful substance. It is a chronic illness characterized by compulsive drug seeking and use. Not every person who experiments with drugs becomes addicted. Addicts begin using voluntarily but because of the changes a substance makes to the brain and body over time, usage becomes a compulsion. The need to use the substance becomes one of the greatest driving forces in the addict’s life. The behaviors associated with attaining the substance cause complications in the individual’s everyday life. It may become impossible to hold a job position or even maintain valued relationships. An addict becomes unable to function normally because the substance abuse rewires neural pathways in the brain, specifically the modules associated with learning and reward and motivation. In addicts, activities that activate the reward center of the brain, including the use of the addictive substance, are repeated. The hypothalamus is a predominate part of the reward center of the brain and it regulates emotional memories and many maintenance activities such as regulating hunger, thirst, and other aspects of homeostasis. The changes made to the hypothalamus and other brain structures during long term substance abuse results in compulsive and destructive behaviors. Addicts learn behaviors that will activate the reward center, including trying other addictive substances. The part of the brain associated with inhibiting behavior is compromised by substance addiction. Over time, an addict requires more and more of the substance to feel the desired effects because a tolerance to the substance develops. Since a tolerance develops to addictive substances over time, it is important for addicts to seek help as soon as possible to avoid a severe addiction and the behaviors associated with use and seeking out the substance. Tolerance is one of the symptoms of physiological dependence. This means that the body requires more of the drug to function normally. Another symptom of physiological dependence to an addictive substance is withdrawal. Withdrawal is characterized by intense cravings of the substance and stressful reactions to the prospect of not receiving more of the drug. Other symptoms can include hallucinations and nausea. In addition to causing physiological dependence, addictive substances can also cause psychological dependence in users. This causes changes in an addict’s emotions and outlook on life. Substance addiction can affect every part of an individual’s social life and career. An addict loses touch with reality when they become dependent on using a substance. The emotional withdrawal symptoms of substance addiction may not seem as severe as the physiological ones, but have a great impact on an addict’s interactions with others. Symptoms of emotional withdrawal from an addictive substance can include anxiety and irritability. The immediate consequences of the compulsive behaviors associated with addiction can be seen in an addict’s interactions with family, friends, and coworkers. This makes these individuals in an addict’s life valuable in the intervention and treatment of the substance addiction. They form the primary support base for an addict on the road to recovery and in aftercare.