Explainer: What are opioids? | Science News for Students

Explainer: What are opioids?

These drugs mimic a natural compound in your brain — with addictive and dangerous impacts
Mar 27, 2018 — 7:22 am EST
opioid drugs
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.

Power Words

(more about Power Words)

addict     An individual that suffers from a disease that provokes the uncontrolled use of a habit-forming drug or uncontrolled or unhealthy habit (such as video game playing or phone texting). Their illness is triggered by brain changes that occur after using some drugs or engaging in some extremely pleasurable activities. People with an addiction will feel a compelling need to use a drug (which can be alcohol, the nicotine in tobacco, a prescription drug or an illegal chemical such as cocaine or heroin), even when the user knows that doing so risks severe health or legal consequences.

addicted     Unable to control the use of a habit-forming drug or to forego an unhealthy habit (such as video game playing or phone texting). It results from an illness triggered by brain changes that occur after using some drugs or engaging in some extremely pleasurable activities. People with an addiction will feel a compelling need to engage in some behavior, such as using a drug (which can be alcohol, the nicotine in tobacco, a prescription drug or an illegal chemical such as cocaine or heroin) — even when the user knows that doing so risks severe health or legal consequences.

antagonist      (in medicine or biology) A substance that blocks or interferes with the normal biological action of another chemical.

anxiety     A nervous reaction to events causing excessive uneasiness and apprehension. People with anxiety may even develop panic attacks.

cell     The smallest structural and functional unit of an organism. Typically too small to see with the unaided eye, it consists of a watery fluid surrounded by a membrane or wall. Depending on their size, animals are made of anywhere from thousands to trillions of cells.

chemical     A substance formed from two or more atoms that unite (bond) in a fixed proportion and structure. For example, water is a chemical made when two hydrogen atoms bond to one oxygen atom. Its chemical formula is H2O. Chemical also can be an adjective to describe properties of materials that are the result of various reactions between different compounds.

diarrhea    Loose, watery stool (feces) that can be a symptom of many types of microbial infections affecting the gut.

endorphins     Any of a group of chemicals secreted within the brain and nervous system. As neurotransmitters, they relay messages within the nervous system. They also activate the feel-good receptors in the body and can raise an individual’s threshold for pain.

heroin     A highly addictive and illegal drug derived from morphine, a potent pain killer. People often take heroin as a narcotic — something that dulls the senses, relieves pain and makes them sleepy or unmotivated to do anything other than lay in a slump.

medulla   A site in the brain located where the brain meets the spinal cord. It controls breathing, heart rate and blood pressure.

methadone    An opioid drug used to treat addiction to more dangerous opioids, such as morphine, heroin or fentanyl. This drug is used to treat pain as well. Methadone binds to the same receptors as other opioids. But it binds very slowly so that the person taking it does not derive pleasure from it. Methadone also lasts a very long time, so a patient will not experience withdrawal. Patients take methadone so that they can stay away from other opioid drugs.

molecule     An electrically neutral group of atoms that represents the smallest possible amount of a chemical compound. Molecules can be made of single types of atoms or of different types. For example, the oxygen in the air is made of two oxygen atoms (O2), but water is made of two hydrogen atoms and one oxygen atom (H2O).

naloxone     A drug that works as an antidote to help people who take dangerous amounts of heroin or some other opiate drug. Naloxone works by binding to the same features on brain-cell surfaces that heroin or related drugs do. This reduces or turns off the pleasurable sensations that opiate drugs would normally produce.

nausea     Feeling sick to one's stomach, as though one could vomit.

nerve     A long, delicate fiber that transmits signals across the body of an animal. An animal’s backbone contains many nerves, some of which control the movement of its legs or fins, and some of which convey sensations such as hot, cold or pain.

neurotransmitter     A chemical released at the end of a neuron to carry a message to a neighboring cell. This chemical travels across the space between two cells, and then binds to molecules on a neighboring cell to transmit a message. Neurotransmitters are released from neurons, and can bind to neurons or to other types of cell, including those that make up muscles or glands.

opioid     Drugs or natural substances that act on receptors (cell molecules) that can block pain signals from traveling along nerves. It can also cause euphoria, intense, pleasurable feelings of well-being. Opioids take their name from opium, a strong painkiller, which was first made from poppies, a types of flower.

overdose     To eat or drink more than the recommended amount of something that may be toxic, such as alcohol or medicines.

pons     A part of the brain that helps to control sleep, breathing, swallowing, urination, hearing, taste and more. It is a spot deep inside at the very base of the brain.

receptor     (in biology) A molecule in cells that serves as a docking station for another molecule. That second molecule can turn on some special activity by the cell.

symptom     A physical or mental indicator generally regarded to be characteristic of a disease. Sometimes a single symptom — especially a general one, such as fever or pain — can be a sign of any of many different types of injury or disease.

tolerance  (In medicine) A condition that can develop in response to repeated doses of a drug, whereby an organism now becomes less sensitive to — more tolerant of — the drug’s effects. A person or animal now needs to take more of a drug than before to achieve the same effect. Tolerance can be one sign of drug abuse.

withdrawal     (in medicine) An almost disease-like syndrome that can develop after animals (including people) attempt to stop using a drug (including alcohol) to which they have become addicted. Shaking, sweating, trouble sleeping, anxiety, diarrhea, vomiting, abdominal cramping, muscle aches and flu-like symptoms can occur and last for days.


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Website: U.S. Department of Health and Human Services. “About the U.S. Opioid Epidemic.” Last updated March 6, 2018.

Website: The Substance Abuse and Mental Health Services Administration. “Naltrexone.” Last updated September 12, 2016.