Explainer: What are opioids?

These drugs mimic a natural compound in your brain — with addictive and dangerous impacts


Opioid drugs such as morphine, fentanyl and heroin can free us from pain. But they have a dark side that can harm.


The “opioid crisis” has made a lot of news — and for good reason. In 2016 alone, more than 42,000 people in the United States died from overdosing on these drugs. Another 2.1 million people became addicted to these painkillers. The drugs’ deadliness comes from the way they affect the brain and other parts of the body. But these drugs have great value, too. They are, after all, some of the best painkillers known.  

Opioids include drugs such as morphine, heroin, fentanyl and oxycodone. The term “opioid” comes from the word “opium.” It’s a chemical that comes from poppies. For thousands of years, opium has been used to treat pain. And through the years, people also have used and abused it for pleasure.

All of these drugs work by impersonating brain chemicals known as endorphins (En-DOR-fins). Endorphins serve as messengers between nerve cells. As such, they are neurotransmitters.

When one brain cell releases endorphin molecules, they float across a gap to another cell. There they bind to receptor molecules. These sit on the outside of the target cell. The endorphin’s shape fits into the receptor like a key into a lock. When they connect, the receptor now can turn on — or off — activities inside its host cell.

Receptors for endorphins exist in the brain’s pleasure center and on nerve cells that relay pain signals. So when the body releases its natural endorphins, they not only fight pain but also contribute to a feeling of pleasure.

Opioids, however, are much, much more powerful than our puny endorphins. People who take opioids can experience intense pleasure and even joy. Opioids also fight pain far more effectively than do our bodies’ natural chemicals.

Here’s the problem

The intense pleasure that opioids produce means that people may want to try them again. And again. As someone takes these drugs more and more often, the body will grow tolerant of the drug. With time, the body will need more and more of an opioid to feel good again.

Each time the effect of an opioid wears off, the person will suffer from withdrawal. Symptoms of withdrawal can include nausea, vomiting, diarrhea, sleep problems, anxiety and more.

What relieves those symptoms? More opioids. The longer a person takes an opioid, they will often need to take more — and bigger — doses to avoid feeling sick. They may then become addicted to the drugs and unable to control their use.

Opioid addiction isn’t cured easily. Some doctors prescribe drugs like methadone (METH-uh-doan) or buprenorphine (BU-preh-NOR-feen) to treat opioid addition. These drugs are also opioids, but they work very slowly, which helps opioid addicts avoid the misery of withdrawal. These drugs also can’t provide the “high” people get from fentanyl or heroin. Doctors might also prescribe naltrexone (Naal-TREX-oan). This drug blocks receptors so that opioid drugs can’t enter them. Naltrexone thus keeps users from deriving pleasure from opioids.

It’s very easy to overdose on opioids. And here’s one reason. There are opioid receptors on areas of the brain called the medulla and the pons. Both areas help control how deeply and frequently someone breathes. By binding to these receptors, opioid drugs can slow breathing. At high enough doses, breathing will stop. 

To prevent this, doctors and emergency workers may inject a drug called naloxone (Nah-LOX-oan), or Narcan. This is an opioid antagonist. That means it binds to the opioid receptors but does not turn them on. By taking the place of the opioid drugs, naloxone can speed breathing back up again — and save someone’s life.

If opioids are so dangerous, why do doctors continue to prescribe them? Pain control. These are simply some of the best painkillers available, especially for severe pain.

Scientists are searching for safer painkillers. An ideal drug would eliminate pain without offering the pleasure of opioids. But it may be many years before such treatments become available.

Bethany Brookshire was a longtime staff writer at Science News Explores and is the author of the book Pests: How Humans Create Animal Villains. She has a Ph.D. in physiology and pharmacology and likes to write about neuroscience, biology, climate and more. She thinks Porgs are an invasive species.

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