What Do Opioids Do to the Brain?

If you’ve ever taken a prescription opioid after having surgery or getting injured, you know how powerful it can be. Opioids can ease pain, calm stress, and bring instant relief. Doctors prescribe opioids such as oxycodone, morphine, codeine, and hydrocodone to treat severe pain. Other opioids, like heroin or fentanyl, are often sourced illegally. Whether or not they come from a pharmacy, all opioids act on the same brain systems.

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In this article, we’ll look at how opioids work in the brain and body, blocking pain and creating feelings of euphoria. We’ll also explain how they can lead to opioid dependence, tolerance, and withdrawal. Finally, we’ll explore how long-term use changes decision-making and motivation, as well as why recovery can take time.

The Brain’s Opioid System

The human brain has its own natural opioid system, which helps the body handle pain, deal with stress, and experience moments of calm or pleasure. The opioid system also plays a role in other bodily functions related to the lungs, heart, and digestive system.

The body makes its own natural opioids, called endorphins, which act like homemade pain relievers. These chemicals are released during activities such as exercise and laughter or in response to pain. Endorphins then attach to opioid receptors — special proteins on neurons (nerve cells) — to help reduce pain and boost feelings of well-being.

Opioid Receptors

Think of an opioid receptor as a lock and an opioid (whether natural or a drug) as a key. When the key fits the lock, the receptor gets activated and tells the nerve cell to do its job. In the opioid system, that job might be “turn down pain” or “turn up pleasure.”

There are three main types of opioid receptors:

• Mu receptors — Reduce pain and create feelings of pleasure
• Kappa receptors — Affect stress response and discomfort
• Delta receptors — Influence mood and emotions

These three types are found throughout the brain and spinal cord and in the gut. Together, they form the body’s built-in system for pain management, stress control, and well-being.

How Opioids Work in the Brain

Natural opioids come from the poppy plant (also called the opium poppy) and have been used for pain relief for centuries. Synthetic (artificial) opioids are made in labs but act the same way. When someone takes an opioid drug, it moves through the bloodstream and into the brain. There, it attaches to opioid receptors — the same ones that endorphins act on. However, unlike the body’s short bursts of endorphins, opioid drugs flood the system and hold on tightly to their receptors.

Creating Powerful Pain Relief

Opioids bind tightly to their receptors, producing effects that go far beyond the body’s natural response. This powerful connection provides strong pain relief. Opioids block pain messages as they travel from nerves in the body, through the spinal cord, and up to the brain. It’s like cutting the wires on an alarm system — the pain is still there, but the brain doesn’t “hear” the signal.

Generating Feelings of Euphoria

Opioids also cause a surge of dopamine, a chemical released by the brain’s reward system. Dopamine’s functions include acting as the brain’s “feel-good” signal. Opioids trigger a much greater dopamine release than naturally enjoyable activities like eating or laughing.

This flood of dopamine creates feelings of euphoria. For many people, the experience is powerful and memorable, and the brain quickly learns to seek it again. That’s why even short-term use of opioids can lead to repeated drug use, cravings, and, in some cases, substance use disorder.

Why Pleasure Turns Into Craving

At first, opioids may seem to solve a problem — pain resolves, stress lifts, and the body relaxes. But inside the brain, something else is happening. Each time opioids trigger a surge of dopamine, the brain’s reward system learns that this drug is an easy shortcut to pleasure.

The brain is naturally wired to repeat behaviors linked to strong rewards. Normally, this system promotes survival by motivating an individual to seek food, safety, and connection with others. Opioids hijack this pathway, producing a reward signal much stronger than the dopamine from enjoyable day-to-day activities. Over time, the brain may begin to prioritize drug-seeking behavior over even basic needs.

Short-Term Effects of Opioids

Opioids affect many of the body’s basic functions. One of the most immediate effects is slowed breathing. In small doses, this may cause mild drowsiness. At higher doses, breathing can become so shallow that oxygen levels drop to a dangerously low level — a condition called respiratory depression. This is one of the main reasons opioid overdoses can be life-threatening.

In addition, opioids slow movement in the digestive tract, which often causes constipation. They can lower blood pressure, leading to lightheadedness or fainting, and affect coordination, raising the risk of falls or accidents. Even at prescribed doses, some people feel unusually sleepy or confused.

Long-Term Effects of Opioid Use

Long-term use of opioids reshapes how the brain and body function. Because opioids act on the brain’s reward system, repeated exposure teaches the brain to expect the drug. Over time, the natural balance of brain chemistry changes.

One of the biggest effects is on decision-making and motivation. Normally, the brain’s prefrontal cortex (PFC) — the part that helps with planning, judgment, and self-control — maintains strong control over other areas of the brain. However, in people with substance use disorder, the PFC becomes less active, and its ability to regulate other areas — like the reward system — weakens. At the same time, the pathways linking pleasure and opioid use get stronger. This imbalance makes it increasingly difficult to resist cravings, even when the drug is causing harm.

Tolerance, Dependence, and Withdrawal

With repeated use, the body adapts to the constant presence of opioids. This leads to tolerance, in which higher doses are needed to achieve the same effect.

Dependence can develop with repeated use, as the body starts to rely on opioids to feel “normal.” Without the drug, a person may experience uncomfortable or painful withdrawal symptoms, including:

• Sweating and shaking
• Nausea
• Flu-like symptoms
• Muscle aches
• Anxiety or agitation
• Intense drug cravings

Tolerance and dependence often reinforce each other. As tolerance builds, the body becomes less responsive to a usual dose, so larger amounts are needed to achieve the same effect. As dependence grows, withdrawal symptoms become harder to manage. Together, these changes create a cycle that makes quitting without an opioid use disorder specialist extremely challenging.

The Dangers of Opioid Misuse

Researchers estimate that between 21 percent and 29 percent of people prescribed opioids for chronic pain will misuse them. Among those, about 8 percent to 12 percent will develop opioid use disorder — a medical condition in which someone continues using opioids despite harmful effects on their health or daily life. OUD reflects real changes in the brain’s chemistry and wiring. Understanding the risks and using opioids carefully can help reduce the chance of it occurring.

One of the most serious dangers of opioid misuse is overdose. Because opioids can slow breathing, taking too much can cause oxygen levels to drop so low that the heart and brain shut down. Overdoses can be fatal, but a medication called naloxone can quickly reverse an opioid overdose if given promptly. Naloxone attaches to opioid receptors, blocking the drug’s effects and restoring normal breathing within minutes — often saving a life.

Other risks of misuse include long-term health problems, a higher chance of infections (especially with injected opioids), and a greater risk of accidents due to drowsiness or confusion.

Healing the Brain After Opioid Misuse

The brain changes caused by opioid misuse are real but not necessarily permanent. With treatment, support, and time, the brain can begin to heal. Recovery may feel slow, but every day without opioids gives the brain more space to forge healthier connections again.

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Have you noticed any of the effects of opioids mentioned in this article in yourself or a loved one? Let others know in the comments below.