The idea of having strong feelings of compulsion to continue taking a drug can be referred to as drug dependence. There are two types of dependence, known as physical dependence and psychological dependence, and they both serve different explanations as to why drug dependence occurs. Physical dependence can occur when trying to avoid the feared consequences of withdrawal. After using a drug, such as heroin or other opioids, it can be difficult to stop using. Therefore, whenever a person discontinues use of the drug, it is common for them to experience physical withdrawal symptoms, such as chills and a fever. The physical symptoms shown during withdrawal can be very severe depending on the various types of drugs. For example, people who abuse alcohol, abstention can cause symptoms such as tremors, weakness, and nausea. But for people who abuse barbiturates, they may experience different physical withdrawal symptoms, such as anxiety, inability to sleep, and lethal convulsions. The other type of dependence, known as psychological dependence, is based on the user’s desire to get the pleasurable effects of the drug. Like physical dependence, psychological dependence also carries withdrawal symptoms, including irritability, insomnia, and depression. While being addicted to substance use, something in the brain triggers the dependency on the drug being used in order to “feel good” even though the person may experience feelings that make them physically sick or feel bad. Although drugs such as heroin and alcohol can induce major physical withdrawal symptoms, there are others that do not, such as nicotine and cocaine. Whether stopping the use of a drug is presented with physical symptoms or not, the patterns are still similar when it comes to compulsive drug-taking behavior.