Opioids affect the brain by binding to its opioid receptors. Chemical receptors are parts of your brain’s chemical messaging system, and they’re located on neurons, the body’s nerve cells. Each chemical receptor fulfills a role when it is activated or stopped. They each bind with chemical messengers called neurotransmitters that can activate their receptors or stop them.
Neurotransmitters that activate a receptor are called agonists, and neurotransmitters that stop or block receptors are called antagonists. Receptors are designed so that only specific chemicals with the right structure can bind to them. Opioids like morphine, heroin, or oxycodone act as opioid receptor agonists, which means they bind to receptors and activate them.
But opioids initially came from opium poppy plants; why are there receptors in the human brain that bind with them?
Morphine, an opioid naturally found in poppy plants, is chemically similar to a neurotransmitter in the brain called endorphins. Morphine was discovered in the 1800s. In the 1970s, scientists found a similar chemical in a cow’s brain and called it endorphins, which is short for “endogenous morphine.” Endorphins are responsible for regulating the body’s pain response. They bind to opioid receptors all over the body and block pain signals from being sent to and received by neurons.
This is designed to help you relax and recover from strain and injuries. Moderate-to-severe pain can get in the way of recovery, so more powerful opioids are used to manage it. It’s unclear why poppy plants have chemicals that bind to receptors in humans and other animals. However, it is clear that these natural substances and the ones humans have created since can have a more profound effect on the human brain.
Opioids activate opioid receptors, which causes sedation and relief from pain. There is even some evidence that the use of opioids during trauma can help reduce a person’s risk of developing post-traumatic stress. However, high enough doses can also cause euphoria and intoxication. Long-term use can lead your brain to adapt to the drug’s presence in your system, changing your natural brain chemistry.
If you stop using, your brain will become chemically imbalanced, causing uncomfortable withdrawal symptoms. Opioid withdrawal is often compared to a particularly bad case of the flu. Because opioid receptors are located throughout your body, and they influence a whole-body system like pain regulation, withdrawal causes symptoms that can be felt all over the body.
Opioids can cause addiction when they start to influence your brain’s reward center. The reward center of the brain is designed to pick up on activities that make you feel good. In most cases, activities that release “feel-good chemicals,” such as dopamine, endorphins, and serotonin, are healthy and life-sustaining.
However, opioids can also influence these chemicals. They mimic your natural endorphins, but they can also trigger the release of extra dopamine, which is a neurotransmitter closely tied to reward. Addiction is characterized as a compulsive desire to use despite the consequences. Opioid addiction is highly difficult to get over on your own, but it is treatable.
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National Center for PTSD. (2019). Opioid Use Among Individuals with Posttraumatic Stress … Retrieved from https://www.ptsd.va.gov/publications/rq_docs/V30N1.pdf
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