The Science of Addiction: How Opioids Affect the Brain

Anyone who takes opioids, whether by prescription or not, is at risk for opioid addition, also known as opioid use disorder (OUD). This is true even if it is a small dose or if it is only taken for a short time. It is impossible to predict who will develop OUD. Many factors play a role, including personal history, genetics, and how long the opioids are used.¹

The Science of Opioid Addiction and the Brain

OUD is the medical term for addiction to opioids. This is a condition where the brain's craving for the drug makes you feel like you've lost control over your actions. While it may have been fun or pleasurable to use opioids in the beginning, addiction can drive you to use drugs even when it is no longer enjoyable.¹

Many substances and habits can lead to addiction. But opioids are especially addictive because of how effectively they disrupt normal brain chemistry.¹

What is OUD?

The terms “opiate” and “opioid” are both used to refer to opioid drugs. Opiates are naturally occurring substances, like the chemicals found in poppy plants. Opioids can be natural chemicals or synthetic chemicals. Opioids include both prescription and illicit drugs, such as:²

• Morphine
• Fentanyl
• Oxycodone
• Tramadol
• Heroin

People living with OUD have strong, often irresistible cravings to use opioids even when they know it may harm themselves or others. Exposure to opioids can change their brain chemistry to make them want these drugs even more.²

OUD is defined as a chronic, relapsing disorder of the brain. It is chronic because it requires lifelong management. It is relapsing because people living with OUD often cycle between periods of opioid use and remission.²

How do opioid drugs change brain chemistry?

Brain cells, called neurons, send and receive messages along neural pathways using chemical signals. Opioids work directly on the brain because neurons have receptors that respond directly to those chemicals. These opioid-sensitive neurons affect:³

• The brain’s reward center
• Mood
• Feelings of anxiety

Opioids may be prescribed to relieve moderate to severe pain, usually after surgery or for diseases like cancer. In the short term, opioids can cause a feeling of relaxation and intense happiness (euphoria). Over time, though, the brain adapts, or builds a tolerance. This can lead to confusion, drowsiness, and trouble breathing.³

How the brain builds a tolerance?

When you take only a small dose of opioids for a short time, the drugs are effective at decreasing pain. But if you take opioids over a longer time, your brain builds up a tolerance to them. You begin to feel like the drugs do not relieve pain as well or do not last as long.³

This shift in brain chemistry happens because neurons change the number of opioid receptors along these neural pathways. You then need more and more opioids to cause the same effect as you used to get from a smaller dose.³

How opioid addiction takes hold in the brain

As opioid use continues, the brain changes in response to it. This makes cravings stronger and stronger. These cravings can become so intense that people living with OUD make choices to get drugs even when it hurts other people.³

Opioid addiction changes brain chemistry over time, making the need for the drug more and more intense. It is like a snowball rolling down a hill, picking up more snow as it rolls.³

Opioids and other addictive substances are said to “hijack” the reward center of the brain. This part of the brain is meant to make us feel happy or satisfied when we do something good for our health and well-being. This might include:²

• Eating when we are hungry
• Using the bathroom when our bladder is full
• Hugging someone we love when we are sad

The reward center of the brain encourages us to keep doing things that keep us healthy. Opioids can take control of this area in 2 ways. They can make the drugs feel like a better choice than healthy things like food or relationships. And they can contribute to relapse by making you feel upset or uncomfortable when you do not take the drugs.²

Recognizing opioid withdrawal symptoms

Once someone has built a tolerance or physical dependence on opioids, stopping them becomes physically and mentally uncomfortable. This discomfort can happen between doses, or when someone is trying to end their addiction (often called detox). Withdrawal causes intense cravings to seek out more opioids. And it leads to physical and emotional symptoms such as:²

• Muscle aches
• Diarrhea
• Sweating
• Racing heart
• Depression
• Anxiety
• Irritability

Can addiction be treated?

Addiction is a chronic disease without a cure, but there are effective treatments. With therapy and medication-assisted treatment (MAT), opioid addiction can go into remission. Research has even shown that the brain changes caused by opioids can be reversed during remission.⁴

If you or a loved one is living with opioid use disorder, please reach out to your doctor to get connected to recovery resources.