The Science of Addiction: How Opioids Affect the Brain

Anyone who takes opioids, whether by prescription or not, is at risk for 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. This is because there can be many contributing factors. These include personal history, genetics, and how long the opioids are used.¹

OUD is the medical term for addiction to opioids. Addiction is a unique condition where you feel as though you lose control over your actions because of your brain’s craving for that drug. 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 work in the brain.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 work on the brain?

Brain cells, or neurons, use chemicals to send and receive messages to and from other areas of the brain or body. Opioids work directly on the brain because neurons have receptors that respond directly to those chemicals. In general, the neurons that respond to opioids in the brain 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). But in the long term, opioids can cause confusion, drowsiness, and trouble breathing. This is because over time, you develop a tolerance to the drugs.³

What is 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

At the level of the brain, this happens because neurons change the amount of opioid receptors they have. You then need more and more opioids to cause the same effect as you used to get from a smaller dose.³

What is addiction?

As opioid use continues, the brain changes in response to it. This makes cravings stronger and stronger. Often, these cravings are so strong that people living with OUD will make choices to get drugs even if it hurts other people.³

Addiction changes the brain over time to make the need for a substance like opioids 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 is an area of the brain whose job it is to make us feel happy or satisfied when we do something that improves 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

What is withdrawal?

Once someone has built a tolerance or physical addiction to opioids, it is physically and mentally uncomfortable to not take them. This may happen in 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), 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.