The two main types of substance use disorders two major categories: abuse and dependence.

Dependence is more severe of the two. Substance dependence involves several features and can occur with most substances. Two of the key features are withdrawal and tolerance. Tolerance means it takes more and more of a substance to get the same effects. For example, someone may start out drinking two 8 oz. cans of beer every night, but later may need four or five cans of beer every night to get the same results. Withdrawal means an individual starts developing physiological or psychological side effects at when stopping use of the substance. Some substances may require medical attention for detoxification and withdrawal. For instance, people withdrawing from alcohol can experience changes in their vitals and possibly seizures. In addition, withdrawal often leads to more substance use to alleviate the symptoms of withdrawal. Besides tolerance and withdrawal, other symptoms from substance use include continuing to use even though the substance has negatively affected one's life. As an example, an individual may receive warnings from his or her doctor that continued alcohol use might result in liver failure, yet the person still continues to use despite this. Cravings, or strong urges for a substance, are also common. Other frequent sign of substance dependence include risk taking behaviors to obtain the substance, requiring a large amount of time to obtain the substance, attempts to stop use that are often unsuccessful, and impairment work, school, and daily activities.

Substance Abuse is not as severe as substance dependence, but it is still dangerous. Substance abuse is repeated use of a substance in a negative way that impacts an individual's daily activities and preferred activities. Use continues even though there are harmful results from it. People often develop substance abuse before they develop substance dependence. Substance abuse also consists of continued use despite legal problems associated with the substance, and social interaction problems.

The substance abuse and dependence disorders include the following:

• Alcohol Abuse/Dependence
  
• Amphetamine Abuse/Dependence
  
• Cannabis Abuse/Dependence
  
• Cocaine Abuse/Dependence
  
• Hallucinogen Abuse/Dependence
  
• Inhalant Abuse/Dependence
  
• Nicotine Abuse/Dependence
  
• Opioid Abuse/Dependence
  
• Phencyclidine Abuse/Dependence
  
• Sedative/Hypnotic/Anxiolytic Abuse/Dependence

People use substances for different reasons. Many people are dual disordered, which means they are diagnosed with both a substance use disorder and a mental health disorder. Often people use substances to self-medicate a mental health disorder. In addition, there is a high number of those who have a past history of trauma and have a substance use disorder. People will often use substances to make flashbacks and anxiety go away. Furthermore, there is also a higher use among relatives. For instance if one's mother or father had a substance use disorder, it is more likely that a son or daughter will develop a substance use disorder. Researchers agree that it is most likely genetic and environmental conditions that contribute to this.