Promethazine

What is Promethazine?

Promethazine is a medication used to treat symptoms of an allergic reaction. It can also be used to prevent motion sickness, nausea, vomiting, and dizziness, as well as to help aid sedation before or after surgery.

It’s a generic medication, meaning it’s not branded, but there is a branded version of it called Phenergan. It’s available as a syrup, tablet, injection, and suppository, but for motion sickness it’s most commonly prescribed as a tablet.

How does Promethazine work?

Promethazine works by stopping your cells from releasing a substance called histamine. Histamine is the chemical that your body releases when it encounters something it perceives to be a threat. Once histamine binds to cells in certain parts of your body, it causes inflammation and other common allergy symptoms, like itching and a runny or stuffy nose.

It also, though, triggers parts of your brain that control nausea and vomiting. So by blocking histamine from binding to its receptors in the brain, Promethazine helps prevent motion sickness when you travel.

What doses of Promethazine are there?

Promethazine tablets are available in three different doses: 12.5 mg, 25 mg, and 50 mg. The usual dosage for adults is 25 mg twice a day, with the first tablet taken 30 minutes to an hour before traveling. You can take another dose eight to twelve hours later if needed.

How to take Promethazine

Take Promethazine half an hour to an hour before traveling, with food, water, or milk to help reduce stomach discomfort.^[1] Swallow your tablet whole, without breaking or chewing it.

You can then take another dose of Promethazine after eight to twelve hours if you need to. For longer trips that last more than a day, you can take promethazine in the morning and before your evening meal during each day of travel.^[2]

Does Promethazine work right away?

Promethazine should work pretty quickly (within half an hour to an hour). Taking it with food will lengthen the time it takes for it to start working.

What should I do if I make a mistake while taking Promethazine?

If you accidentally take too much Promethazine, seek medical help right away or head to your nearest emergency department. If you miss a dose, take it as soon as you can (unless it’s nearly time for your next dose). If it’s close to your next dose, skip the missed dose and carry on as normal – don’t take a double dose to make up for a missed one.