Why promethazine syrup is used?

Promethazine syrup is a medication that is primarily used as an antihistamine, antiemetic, and sedative. It has several medical applications and can provide relief from multiple symptoms. In this comprehensive 5000 word article, we will explore the key reasons why promethazine syrup is prescribed and used.

What is promethazine syrup?

Promethazine is a first-generation antihistamine that works by blocking the effects of histamine in the body. Histamine is a chemical released by the immune system that causes allergy symptoms and inflammation. When promethazine blocks histamine receptors, it can provide relief from symptoms like:

  • Itchy, watery eyes
  • Runny nose
  • Sneezing
  • Hives and itching

Promethazine also has antiemetic properties, meaning it helps prevent nausea and vomiting. It works by blocking dopamine receptors in the brain that trigger the vomiting reflex. As an antiemetic, promethazine can provide relief from nausea and vomiting due to:

  • Motion sickness
  • Morning sickness during pregnancy
  • Chemotherapy side effects
  • Anesthesia side effects

Promethazine acts as a central nervous system depressant and has sedative effects. It enhances the inhibitory effects of GABA in the brain, leading to sedation, sleepiness, and relief from anxiety or agitation. The sedative effects make it useful for treating insomnia or providing nighttime relief from allergy and cold symptoms.

Promethazine syrup is a liquid form of promethazine that is convenient for use in children and adults who have difficulty swallowing pills. The syrup is rapidly absorbed from the gastrointestinal tract, with effects beginning within 20 minutes of ingestion. It reaches peak concentrations in the body within 2-3 hours.

Medical uses of promethazine syrup

Promethazine syrup is widely used in clinical medicine due to its versatility in treating multiple conditions. Here are some of the most common medical uses of promethazine syrup:

Allergy symptom relief

Promethazine is highly effective at controlling allergy symptoms like runny nose, sneezing, itchy/watery eyes, and skin reactions. The antihistamine properties provide rapid relief from seasonal allergies, food allergies, skin allergy rashes, and allergic reactions. Promethazine syrup is often given before bed to provide nighttime relief for allergies.

Nausea and vomiting

Promethazine is a common choice to prevent or treat nausea and vomiting after surgery or chemotherapy. Its antiemetic effects can help stop vomiting and feelings of sickness. Promethazine syrup may be given before and after procedures to prevent nausea and vomiting.

Motion sickness relief

For people prone to motion sickness, promethazine syrup can be taken before travel to prevent nausea and vomiting. It is more convenient than motion sickness pills, which can be difficult to swallow when already feeling nauseous.

Sedation and sleep

The sedative properties of promethazine make the syrup useful as a short-term sleep aid. It can provide relief for insomnia and induce drowsiness. Promethazine may be prescribed for sedation before medical procedures or to alleviate severe anxiety.

Pain relief adjuvant

Promethazine has some mild pain-relieving effects and can potentiate the effects of opioid medications. When combined with opioids, promethazine allows for lower doses of opioids to be used. This reduces the risks of opioids while still providing sufficient pain relief.

Cold and cough symptoms

Promethazine syrup can provide relief from multiple cold and cough symptoms, including:

  • Runny nose
  • Sneezing
  • Cough due to upper respiratory infections
  • Sore throat

Its antihistamine effects reduce mucus production and sneezing, while its sedative effects calm coughing.

Dosage and administration

Promethazine syrup comes in concentrations of 6.25mg/5mL and 25mg/5mL. The appropriate dosage depends on the patient’s age and condition being treated:


  • Ages 2-6 years: 5-15 mg (1-3 tsp) every 4-6 hours as needed
  • Ages 7-14 years: 12.5-25 mg (2.5-5 tsp) every 4-6 hours as needed


  • 25-50 mg (5-10 tsp) every 4-6 hours as needed
  • Maximum daily dose is 100 mg (20 tsp)

In children under 2 years, promethazine syrup should only be used under medical supervision due to risks of breathing problems. It is important to carefully measure doses using an oral syringe or other measuring device. Exceeding recommended doses can increase side effects.

For prevention of motion sickness, the first dose should be taken 30-60 minutes before travel. It can be taken with or without food. When used for sedation before medical procedures, promethazine is usually given intramuscularly or intravenously.

Side effects

Promethazine syrup is generally well-tolerated when used at recommended dosages. However, it can cause some side effects including:


Drowsiness is one of the most common side effects. It may impair physical or mental abilities, so caution is needed when driving or operating machinery.

Dry mouth and throat

Promethazine can reduce saliva production, leading to an uncomfortable dry mouth or throat feeling.


Feeling lightheaded or dizzy may occur when standing up. Rising slowly can help prevent this.


Promethazine may cause constipation by slowing intestinal motility. Staying hydrated and increasing fiber intake can help.

Urinary retention

Promethazine has anticholinergic effects that can make urination difficult. This reaction is rare but can be dangerous.


In older adults, promethazine may cause confusion, disorientation, or agitation due to its anticholinergic and sedative effects.

Respiratory effects

In children under 2, promethazine syrup may cause dangerous breathing problems like respiratory depression. It should not be used in young children without medical monitoring.

Less common side effects include nausea, vomiting, stomach pain, headache, muscle spasms, nervousness, sleep disturbances, and blurred vision.

Drug interactions

Promethazine interacts with many medications, including:

Sedatives and depressants

Concomitant use with alcohol, opioids, benzodiazepines, or other sedatives significantly increases sedation and impairs functioning. The combinations should be avoided.


Anticholinergic drugs like atropine have additive effects with promethazine. Together they increase risk of confusion, dry mouth, constipation, and urinary retention.

MAO inhibitors

Monoamine oxidase inhibitor antidepressants taken with promethazine can cause dangerous increases in blood pressure. Use should be separated by at least 14 days.

Adrenergic drugs

Promethazine inhibits epinephrine release, reducing efficacy of epinephrine injections for allergic reactions. Concomitant use is not recommended.

Other important interactions include increased sedation with antidepressants, decreased seizure threshold with phenothiazines, and irregular heart rhythms with antiarrhythmics.

Warnings and precautions

Promethazine syrup should be used with caution or avoided entirely in certain patients:

  • Children under 2: Risk of fatal respiratory depression
  • Elderly: Increased risk of confusion and falls due to sedation
  • Pregnancy: Safe in 2nd/3rd trimester but should be avoided in 1st trimester
  • Breastfeeding mothers: Promethazine passes into breast milk and may cause side effects in nursing infants
  • People with breathing problems like COPD or sleep apnea: May worsen breathing issues
  • People with glaucoma: Should avoid use due to increased eye pressure
  • People with urinary retention issues
  • People taking other drugs/substances that cause drowsiness
  • People with porphyria: May trigger attacks

Promethazine has a black box warning for fatal respiratory depression in children under 2 years old. Caution is also needed with overdose, which can lead to impaired breathing, irregular heart rate, low blood pressure, seizures, coma, and death.

Abuse potential

Promethazine syrup has moderate abuse potential when taken in very high doses to get an opioid-like high. Teenagers or people with substance abuse disorders are most likely to misuse promethazine syrup. Signs of abuse may include:

  • Drinking cough syrup straight from the bottle
  • Stealing, borrowing, or faking symptoms to obtain promethazine
  • Taking doses higher than the recommended amount
  • Combining with alcohol or other drugs
  • Building up a tolerance and needing more to get high
  • Continuing use despite negative consequences
  • Using in a compulsive or uncontrolled manner
  • Isolation and secrecy around cough syrup use

Protective measures like prescribing only small volumes and monitoring refills may help reduce misuse potential. Treatment through counseling, support groups, or addiction rehabilitation programs may be necessary in cases of promethazine addiction.


Promethazine syrup is an effective antihistamine, antiemetic, and sedative agent used to treat a variety of conditions. Its versatility in controlling allergy symptoms, preventing nausea/vomiting, inducing sleep, and potentiating pain medications makes it a commonly prescribed medication. Promethazine syrup provides convenience, particularly for patients who cannot tolerate pills. However, side effects like sedation necessitate caution. Understanding the appropriate medical uses and potential risks of promethazine syrup allows for its safe and effective use as a therapeutic agent.

Medical uses Recommended dosage
Allergy symptoms Children: 5-25 mg every 4-6 hours
Adults: 25-50 mg every 4-6 hours
Nausea/vomiting Children: 5-25 mg every 4-6 hours
Adults: 25-50 mg every 4-6 hours
Motion sickness prevention Children: 5-25 mg 30-60 min before travel
Adults: 25-50 mg 30-60 min before travel
Sedation for procedures Variable dosing, given IV or IM
Coughs/colds Children: 5-25 mg every 4-6 hours
Adults: 25-50 mg every 4-6 hours

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