Side Effects of Opioid Medication

Opioids are powerful drugs with powerful side effects.

Medically reviewed in April 2021

Opioids—a class of drug that includes oxycodone, hydrocodone and codeine, as well as heroin, morphine and fentanyl—may knock out the pain, but they carry a number of risks and side effects. The changes in brain and body chemistry opioids cause can lead to addiction, but that’s not the only side effect to be aware of.

How opioids work
When you take an opioid, the molecules of the drug attach themselves to opioid receptors, parts of brain, spinal cord gastrointestinal and other cells that act like ports. Think of using a USB connection to sync your smartphone with your computer; the port is the receptor and the cable is the opioid molecule. When the drug activates these opioid receptors, they reduce the sensation of pain.

Various types of opioid receptors that tell the body to turn other functions off or on, like breathing and the brain’s reward system. Take opioids for too long and your body can lose its ability to activate these receptors on its own. And, if you take too much at once your breathing reflex can shut itself off. Even at lower doses opioids can produce side effects in both the brain and other parts of the body.

Physical side effects of painkillers
Constipation is one of the most common side effects of opioids, affecting between 40 and 95 percent of everyone who takes them. Opioid receptors in cells of the gut influence the bowels’ movement, a characteristic called motility, and when you take opioids it slows everything down in the bowels.

Nausea and vomiting are another set of common side effects of opioids, and the dose that can make you feel ill is less than the dose that kills pain. Nausea and vomiting often goes away within a few days or weeks, but for the cases where it doesn’t, naltrexone is often used in combination with painkillers. Other anti-nausea drugs as well as changing the type of opioid or the way it’s delivered may help as well.

Opioids may also leave you feeling sleepy or sluggish. It’s called sedation, and it’s one of the more common side effects of opioids. Healthcare providers can reduce your dose, give you a different opioid or perhaps give you a stimulant medication if sedation is troubling you.

Opioids change your brain
Opioid side effects don’t just affect your body; they affect your brain as well. Long-term use of opioids, defined as more than 30 days, carries the risk of depression, according to a 2016 study in the Annals of Family Medicine. The researchers suggest depression may happen because of brain chemistry changes and a drop in testosterone.

Addiction is one of the most insidious side effects of opioids. They produce a sense of pleasure and euphoria because they work on the sections of the brain that process reward. Addiction produces strong cravings for the drug, and as a result, people who are addicted will do nearly anything to get more. Work can suffer, relationships can fall by the wayside, and the person addicted may engage in risky behaviors like using their medication for longer than prescribed. 

The difference between addiction and dependence
There’s a marked difference between addiction and physical dependence. Withdrawal symptoms like shivering or muscle aches come from physical dependence, but physical dependence is not the same thing as addiction.

After a period of taking opioids, a higher dose is required to get the same effect. That’s tolerance. Because the opioid receptors are continually hammered by higher and higher doses of opioids, they start to function normally only when drugs are in the system. In that case, the user is dependent upon the drugs, and if he or she doesn’t get their dose of opioids, withdrawal symptoms occur.

Addiction, on the other hand, is characterized by the cravings for the drug, which are often so strong that people are unable to stop using the drug even when they know it’s causing them harm. It’s possible to be addicted but not dependent upon opioids—and vice versa—but very often the two go hand in hand.

The bottom line
Opioids are powerful painkilling medications that can be the right choice in certain circumstances. But regardless of the circumstances, it’s important to be educated about the possible side effects of opioids. Always follow your healthcare provider’s instructions, and seek help if you feel or fear that you’re becoming addicted or dependent on the drugs. 

Featured Content


How Does an Opioid Addiction Start?

Understand the physical and mental factors at play—and why overdose deaths are on the rise.

Know the Signs of Opioid Use and Addiction

Spot the telltale signs of an opioid addiction and get help before it’s too late.

5 Ways to Beat Symptoms of Opioid Withdrawal

From acupuncture to opiate withdrawal medications—there are a lot of alternatives to going "cold turkey."

9 Keys to Safe Opioid Use

Opioids are powerful pain meds that can be extremely addictive. See how to dodge common opioid pitfalls and stay safe.

Opioid-Free Ways to Beat Pain

Acetaminophen and ibuprofen may work just as well—and sometimes better.