Opioid dependence is an addiction disorder characterized by the systematic abuse of an opiate analgesic drug. The following drugs are the most commonly abused opiates: heroin, oxycodone, hydrocodone, morphine, and codeine. Heroin is the world's most commonly abused opiate drug, primarily because of the intense euphoria it produces. Chronic abuse of one or more of these substances leads to physical dependence and psychological addiction. Opiate analgesics can be smoked, snorted, or injected.
When an individual abuses an opiate drug for a lengthy period of time, physical opioid dependence may occur. For example, if he injects heroin on a daily basis for a sustained period of time, he is likely to start experiencing intense physical withdrawal symptoms when the drug is stopped. Typical physical withdrawal symptoms include nausea, vomiting, diarrhea, stomach cramps, muscle aches, insomnia, fever, suicidal depression, and anxiety. The aforementioned physical withdrawal symptoms are common to all forms of opiate analgesic, with varying degrees of severity.
In terms of the biochemistry of opioid dependence, the main reason opiate drugs are highly addictive is that they bind to opiate receptors in the brain. These receptors are designed for a molecule known as endorphin, which increases feelings of pleasure and decreases feelings of pain. On administration, the opiate drug mimics the action of the endorphin neurotransmitter and produces an intense feeling of euphoria. When a person takes an opiate drug for lengthy period of time, the brain stops producing endorphins because the receptors are overloaded with the opiate drug. Therefore, when a person stops using an opiate, such as heroin, the lack of endorphins and the absence of the opiate will produce extremely painful withdrawal symptoms.
One of the more severe forms of opioid dependence is long-term heroin addiction. Long-term heroin addicts are terrified of experiencing the aforementioned withdrawal symptoms and will go to almost any lengths to acquire the drug. Typically, the long-term heroin addict will use the drug for the purpose of feeling "normal" and avoiding withdrawal. Some addicts have heroin habits of up to $500 US Dollars (USD) per day, in which case he or she may be reduced to stealing, dealing drugs or acquiring funds via prostitution to pay for the drugs. Developed countries have opioid dependence medical treatment programs in place for addicts who wish to recover, including programs in which an addict is prescribed methadone to help with the withdrawal symptoms.