Phenergan side effects: common problems and safety tips

Phenergan (promethazine) is a strong antihistamine often used for nausea, allergies, and motion sickness. It helps many people, but it can cause side effects that matter—especially if you’re taking other medicines, are elderly, or giving it to a child. Here’s a clear, practical look at what to expect and what to watch for.

What you’ll likely notice

The most common effects are easy to spot: drowsiness, dizziness, and dry mouth. Many people feel sleepy or slow after a dose—so avoid driving or operating machines until you know how it affects you. Other routine issues include blurred vision, constipation, and mild lightheadedness when standing up.

Those side effects usually fade as your body adjusts. Drinking water for dry mouth, standing up slowly for dizziness, and avoiding alcohol can help a lot.

Serious side effects and red flags

Some reactions need urgent care. Call emergency services or your doctor if you get trouble breathing, severe chest pain, fainting, very fast or irregular heartbeat, or a high fever with stiff muscles. Also seek help if you notice extreme confusion, uncontrollable jerking or restlessness, or sudden severe skin reactions.

Kids and older adults are more at risk. Promethazine can cause dangerous breathing problems in infants and strong sedation in elderly people. Don’t give Phenergan to children under two years old, and talk to a doctor before giving it to children under six.

There are medical conditions that make Phenergan risky. Tell your prescriber if you have glaucoma, enlarged prostate (urinary problems), breathing issues like COPD or asthma, heart rhythm problems, liver disease, or a history of seizures.

Drug interactions matter. Phenergan adds to the sedative effect of opioids, benzodiazepines, alcohol, and other sleep medicines—this can slow breathing. It can also react badly with MAO inhibitors and certain antidepressants or heart drugs that affect rhythm. Always list all your medications to your provider or pharmacist.

How to reduce risk: use the lowest effective dose for the shortest time, avoid alcohol and recreational drugs, and don’t mix with strong sleep medicines unless your doctor approves. If you feel very sleepy or off balance, skip driving and call your prescriber to adjust the dose.

Pregnancy and breastfeeding decisions should involve a clinician. Promethazine is sometimes used for nausea in pregnancy, but risks and alternatives should be weighed by your doctor.

Final quick checklist: know the common side effects, watch for breathing problems or sudden confusion, avoid alcohol and opioids while taking Phenergan, and ask your doctor about safer options if you’re elderly, pregnant, or giving it to a child. If in doubt, contact healthcare right away—better safe than sorry.