Common Opioid Side Effects: Constipation, Drowsiness, and Nausea

When doctors prescribe opioids for severe pain-after surgery, cancer treatment, or a major injury-they’re not just giving you relief. They’re also giving you a set of predictable, often stubborn side effects. For many people, constipation, drowsiness, and nausea become part of daily life while taking these medications. Unlike a headache or a rash, these aren’t temporary annoyances. They stick around. And if you don’t plan for them, they can make life harder than the pain you’re trying to treat.

Constipation: The Most Common, and Most Overlooked, Side Effect

If you’re on opioids long-term, constipation isn’t a possibility-it’s a guarantee. Studies show nearly every patient who takes opioids for more than a few weeks will experience it. Why? Because opioids don’t just block pain signals in your brain. They also latch onto receptors in your gut, slowing down the natural muscle contractions that move food through your intestines. The result? Stools become hard, dry, and painfully difficult to pass.

Unlike drowsiness or nausea, which often fade after a week or two, constipation doesn’t improve with time. Your body doesn’t build tolerance to it. That’s why experts say you shouldn’t wait until you’re struggling to go. Start treatment for constipation the same day you start opioids. Prophylactic laxatives aren’t optional-they’re essential.

The most effective approach combines two types of laxatives: a stimulant like senna to get things moving, and an osmotic agent like polyethylene glycol to pull water into the colon. Drink plenty of fluids. Eat fiber-rich foods. Stay active. These help, but they’re rarely enough on their own. If over-the-counter options fail, medications like methylnaltrexone (Relistor) or naloxegol (Movantik) are designed specifically for opioid-induced constipation. They work in the gut without touching the pain-relieving effects in your brain.

Ignoring constipation doesn’t just make you uncomfortable. It can lead to bowel obstruction, hemorrhoids, or even hospitalization. Don’t wait until it’s severe. Talk to your doctor before your first dose.

Drowsiness: When Your Brain Feels Like It’s Wading Through Mud

You take your opioid, and suddenly everything feels slower. Your thoughts are foggy. Your eyelids are heavy. You feel like you’ve been up for three days-even if you slept eight hours. That’s not laziness. That’s the drug working exactly as it’s supposed to. Opioids depress the central nervous system. That’s how they reduce pain. But it also reduces alertness.

Between 20% and 60% of people starting opioids report drowsiness. For most, it fades after a few days as the body adjusts. But for about 1 in 10 long-term users, the fog never lifts. That’s a problem if you drive, work with machinery, or care for children. Even mild drowsiness increases the risk of falls and accidents.

The key is timing. Take your dose at night if possible. Avoid alcohol, benzodiazepines like Xanax, or sleep aids-they multiply the sedation and can be deadly. If drowsiness persists beyond two weeks, don’t just push through it. Talk to your doctor. A small dose reduction might help. In rare cases, stimulants like methylphenidate (Ritalin) are used off-label, but there’s little solid evidence they work consistently, and they come with their own risks.

Also, review all your other medications. Some antidepressants, antihistamines, and muscle relaxants make drowsiness worse. Eliminating unnecessary drugs can make a big difference.

Nausea: Why Your Stomach Feels Like It’s in Revolt

Nausea hits about one in four people when they start opioids. It’s not just feeling queasy-it’s the urge to vomit, often without warning. The reason? Opioids trigger a part of your brain called the chemoreceptor trigger zone. They also slow down your stomach emptying, which makes food sit and ferment, adding to the discomfort.

The good news? For most people, nausea fades within 3 to 7 days. Your body adapts. But for 1 in 10 long-term users, it doesn’t. And when nausea sticks around, it makes people skip doses-or stop the medication entirely. That means uncontrolled pain. That’s the opposite of what you want.

Treatment starts with anti-nausea meds. The most common first choice is metoclopramide or prochlorperazine-drugs that block dopamine, one of the main triggers. If those don’t work, ondansetron (Zofran), which targets serotonin, can help. Promethazine (Phenergan) is another option, especially if you’re also having trouble sleeping.

Don’t try to tough it out. If nausea lasts more than a week, ask for help. Your doctor can switch you to a different opioid. Some, like tramadol or buprenorphine, are less likely to cause nausea. Or they can adjust your dose. Starting low and going slow-taking a smaller dose at first and increasing it gradually-is the best way to avoid severe nausea from the start.

Why Managing These Side Effects Matters More Than You Think

It’s easy to think of these side effects as just part of the deal. But they’re not harmless inconveniences. They’re major reasons people stop taking opioids-or start misusing them.

The CDC reports that more than two-thirds of people who misuse prescription opioids do so because they’re trying to relieve physical pain. If constipation is so bad you can’t leave the house, if drowsiness makes you useless at work, if nausea keeps you from eating-you might be tempted to take more than prescribed just to feel normal. Or worse, you might turn to street drugs.

And if you suddenly stop opioids because the side effects are unbearable? That can trigger withdrawal: vomiting, diarrhea, sweating, anxiety, and intense pain. The FDA warns that abrupt discontinuation can lead to serious harm, including suicide.

Managing side effects isn’t about comfort. It’s about safety. It’s about keeping you on the right treatment so you don’t end up in a worse place.

What You Can Do Today

If you’re on opioids, here’s your action plan:

• For constipation: Start a daily laxative regimen the same day you start opioids. Use a stimulant + osmotic combo. Drink 8-10 glasses of water daily. Walk for 20 minutes every day.
• For drowsiness: Take your dose at night. Avoid alcohol and sedatives. Review all other meds with your doctor. If you’re still foggy after two weeks, ask about a dose adjustment.
• For nausea: Don’t wait. Ask for an antiemetic on day one. If it doesn’t help in 3-5 days, try a different class. Consider switching to a different opioid if nausea persists.

Keep a simple log: note when you take your opioid, when side effects hit, and how bad they are. Bring it to your next appointment. It’s the fastest way to get help.

When to Call Your Doctor

Not every side effect needs an emergency room. But some do. Call your doctor right away if you experience:

• Not having a bowel movement for 4 or more days
• Severe drowsiness where you can’t stay awake or wake up easily
• Vomiting that lasts more than 24 hours or includes blood
• Confusion, slurred speech, or slow, shallow breathing

These could signal overdose or dangerous interactions. Don’t wait.

Next Steps

If you’re currently on opioids and struggling with side effects, don’t suffer in silence. Schedule a visit with your doctor. Bring your symptom log. Ask about: a laxative plan, a dose adjustment, or switching to a different opioid. There are safer, more manageable ways to control pain without letting side effects take over your life.