Scrambled systems
The answer is in the human brain. Opioids activate several brain systems, including one that motivates a person to take more of the drug. At the same time, opioids cause changes in another part of the brain that limits a person’s ability to stop taking them.

When these two brain processes work in combination, the effect is like hitting the accelerator in a car—without having any brakes. A person addicted to opioids feels an intense urge to take the drug again, and also has a hard time resisting that urge.

Opioids on repeat
The longer someone misuses opioids, the less self-control the person will have; it gets more and more difficult to resist taking the drug, or to follow through on a resolution to quit. Opioids diminish the person’s ability to make a different choice. Their brain is like a car that, besides having no brakes, has a steering wheel that works poorly—or doesn't work at all.

Because prescription opioids can affect a person in such powerful ways, you should only use them exactly as prescribed. Otherwise, you risk letting a drug take control of your brain.


Source: NIDA