Promethazine is a drug used to treat allergies, dizziness, nausea, and vomiting.

Doctors sometimes prescribe it to help people relax or fall asleep in hospital settings. Doctors may also prescribe it off-label to treat anxiety.

This article explores how promethazine works, as well as current research into its safety and effectiveness in treating anxiety.

Promethazine is an antihistamine. That means it blocks the effects of histamine, a chemical involved in allergic reactions.

Your immune system makes and releases histamine when it detects an allergen like pollen or pet dander. By blocking the effects of histamine, promethazine helps relieve allergy symptoms such as nasal congestion and itchy eyes.

Promethazine also has several other effects throughout the body. For example, it helps with motion sickness by blocking specific receptors in the medulla oblongata, a part of the brain involved in nausea and vomiting.

It also targets other brain receptors involved in blood pressure, sleep, and muscle tension.

There are no recent clinical studies assessing how effective promethazine is in treating anxiety. This makes it impossible to say how it compares to other anti-anxiety drugs.

With that said, it is approved by the Food and Drug Administration (FDA) for sedation. According to its label, it eases apprehension and triggers a gentle sleep.

Medical professionals may administer it in hospital settings to reduce anxiety and induce sleep before or after surgery. A 2015 review reports that when used prior to surgery, promethazine can relieve anxiety.

Other peer-reviewed articles suggest that, when used alongside other drugs, promethazine may help treat acute mental health issues.

For example, the authors of a 2019 article recommend promethazine use with the antipsychotic drug haloperidol to treat severe agitation in psychiatric care settings. In this case, promethazine protects against side effects caused by haloperidol.

A 2016 review states that there’s enough evidence to use haloperidol and promethazine to treat episodes of severe aggression caused by schizophrenia. The authors write that promethazine can help to cause drowsiness and reduce “nervous tension.”

There isn’t enough evidence to show that promethazine is useful in treating mild to moderate anxiety outside hospital settings. It’s also not FDA-approved for this use. But you can always talk with your doctor if you think promethazine might help with your symptoms.

The main side effect of promethazine is drowsiness. If you take it during the day, you might feel lethargic or have trouble staying awake. For this reason, you shouldn’t drive or operate heavy machinery after taking promethazine.

Some other possible side effects include:

  • blurred vision
  • confusion and disorientation
  • constipation
  • difficulty urinating
  • dilated pupils
  • dizziness
  • dry mouth
  • headaches
  • muscle contractions
  • nightmares
  • poor coordination
  • restlessness
  • stiffness

Many adults can safely take promethazine as prescribed by a doctor. It may pose increased risks for people who:

Promethazine can interact with other drugs, especially:

Be sure to tell your doctor or pharmacist if you’re taking other medications.

You should also avoid drinking alcohol while taking promethazine. It can make side effects like drowsiness and sedation worse.

Is promethazine safe for children?

Promethazine is not safe for children younger than 2 years, as it can cause severe respiratory problems and even death.

In children older than 2 years, promethazine should be used carefully according to a doctor’s instructions. Parents shouldn’t use it to treat nausea and vomiting that has an unknown cause.

Children under the age of 16 should not take promethazine medications with codeine or other pain relievers.

What is the typical dose for promethazine to treat anxiety?

According to StatPearls, the recommended dose of promethazine for adults to help with anxiety and sleep before or after surgery is 25 to 50 milligrams (mg). Your doctor will determine the appropriate dose of promethazine for you.

How quickly does promethazine work?

How quickly promethazine works depends on its method of administration. In general, it should work within 30 minutes. Injections may work slightly faster.

Can I take promethazine with other anxiety medications?

No, you should not take promethazine with other anxiety medications, as this could increase your risk of side effects. Talk with your doctor to learn more about which medications are safe to take with promethazine.

In what forms is promethazine available?

Promethazine is available in several forms, including:

  • an injectable solution
  • a drinkable solution
  • a rectal suppository
  • a syrup
  • tablets

Is promethazine available over the counter?

Promethazine is not available over the counter in the United States. You need a prescription from a doctor to take promethazine.

Promethazine is a prescription drug used to treat nausea, vomiting, and allergies. You may also receive it while in the hospital to relieve anxiety and trigger sleep.

When combined with the drug haloperidol, evidence suggests it can ease severe aggression and agitation.

The FDA has not approved promethazine for mild to moderate cases of anxiety outside of medical settings, and it’s unclear whether it’s effective for this use. It causes significant drowsiness, which could interfere with your ability to function during the daytime.

If you have anxiety, talk with your doctor to learn more about available medications and treatments.