Drug addiction is a cycle that moves continuously through three distinct stages: Intoxication, Withdrawal, and Anticipation. The intoxication phase occurs when an individual actively takes a drug. The length of this stage depends on the drug in question. As the drug is metabolized and is no longer present in the body, the individual enters withdrawal, where the absence of the drug produces different effects. Withdrawal is often characterized by negative moods due to the unhappiness of coming down from a high. Finally, the anticipation phase occurs when an individual craves the drug and begins to feel excited and preoccupied with planning their next drug use.
Executive function is the ability to make rational decisions. It is generally governed by the prefrontal cortex (PFC) area of the brain. Executive function is essential to the addiction cycle as it drives the craving of the drug that prompts a person to continue drug use. Additionally, executive function regulates the absence of reward that is felt during withdrawal, when the drug is not present.
After administering a drug multiple times, an individual may develop tolerance to that drug or drugs in the same family. If you’ve ever had alcohol on multiple occasions, you may know what tolerance is. Tolerance is the developed need for larger doses of a drug to produce the same behavioral or physiological effects. Different opioids, if they operate on the brain with similar mechanisms, can produce tolerance for each other. For example, if you have developed a tolerance for heroin, you would also have tolerance for morphine, even if you’ve never been exposed to morphine before. People with opioid tolerance might no longer experience some of the effects of opioids like decreased breathing or death. However, these same individuals might have worsened constipation, insomnia, excessive sweating, calmness/sleepiness, and pupil constriction.