How long does promethazine take to work? Promethazine will start to make you feel sleepy around 20 minutes after you take it and may work for up to 12 hours. If you’re taking it for a cough or cold, allergies or feeling sick (nausea), your symptoms should start to improve within 20 minutes. The medicine should work for around 4 to 6 hours.
Promethazine is known as a drowsy (sedating) antihistamine as it makes you sleepy.
Most people prefer to take a non-drowsy antihistamine as it’s less likely to interfere with their everyday routine.
You might choose to take a drowsy antihistamine, however, if you’re having problems falling asleep, or if symptoms like itching or coughing are keeping you awake.
There is not enough information available to say whether one antihistamine is better than another for treating allergies.
You may need to try a few different medicines to find what works best for you. Ask your pharmacist or doctor for advice if you’re unsure.
See also Warning section.Promethazine is used to prevent and treat nausea and vomiting related to certain conditions (such as before/after surgery, motion sickness). It is also used to treat allergy symptoms such as rash, itching, and runny nose. It may be used to help you feel sleepy/relaxed before and after surgery or to help certain opioid pain relievers (such as meperidine) work better. It may also be used for a short time to treat a runny nose due to the common cold.Promethazine is an antihistamine and works by blocking a certain natural substance (histamine) that your body makes during an allergic reaction. Its other effects (such as anti-nausea, calming, pain relief) may work by affecting other natural substances (such as acetylcholine) and by acting directly on certain parts of the brain.Cough-and-cold products have not been shown to be safe or effective in children younger than 6 years. Therefore, do not use this product to treat cold symptoms in children younger than 6 years unless specifically directed by the doctor. Some products (such as long-acting tablets/capsules) are not recommended for use in children younger than 12 years. Ask your doctor or pharmacist for more details about using your product safely.These products do not cure or shorten the length of the common cold and may cause serious side effects. To decrease the risk for serious side effects, carefully follow all dosage directions. Do not give other cough-and-cold medication that might contain the same or similar ingredients (see also Drug Interactions section). Ask the doctor or pharmacist about other ways to relieve cough and cold symptoms (such as drinking enough fluids, using a humidifier or saline nose drops/spray).