The generic version of antihistamine Phenergan, Promethazine is used for treating allergic reactions and sedating women during labor and before and after surgery. But it has been linked to numerous side effects, including fatal respiratory depression in children and gangrene.

Promethazine Pills
Promethazine Facts
  1. Dosage Available as pill, suppository and injectable: 12.5 mg, 25 mg, or 50 mg
  2. Used to Treat Allergic reactions and to sedate patients before and after surgery and during labor, to prevent and control nausea and vomiting
  3. Interactions Alcohol, sedatives or hypnotics, narcotics, general anesthetics and tricyclic antidepressants
  4. Related Drugs Phenergan, Phenadoz and Promethegan
  5. Black Box Warnings Issued in 2004 for fatal respiratory depression in children less than 2. Another issued in 2009 for severe chemical irritation and tissue damage
  6. FDA Approval 1951
  7. Active Ingredient Promethazine hydrochloride

Promethazine, an antihistamine initially developed in France in the 1940s, was approved for the U.S. in 1951. The drug is not only used in the treatment of allergic reactions, such as hay fever, but it can also be used as a sedative, to prevent motion sickness, and to combat nausea and vomiting (including morning sickness).

A year after it entered the U.S. market, a combination drug of promethazine hydrochloride and codeine (a prescription narcotic) was introduced for common-cold symptoms and cough. However the substance has also been misused as a potentially dangerous illegal street drug called “drank.”

Promethazine Administering Methods
Promethazine can be administered orally as a tablet, through the rectum as a suppository and intravenously by injection

Along with its liquid form, promethazine can be administered orally as a tablet, through the rectum as a suppository and intravenously by injection. But injection problems have linked the drug to severe tissue injuries, including gangrene.

This prompted a black box warning (the most serious drug labeling warning) from the U.S. Food and Drug Administration in late 2009. This was the second black box warning for the antihistamine drug, with the first being required in 2006 after the FDA received reports of fatal respiratory depression (inadequate ventilation or increased concentrations of carbon dioxide) in children.

These severe, potentially life-threatening conditions are in addition to the long list of side effects, both common and serious, linked to promethazine, which still remains in popular demand, with the FDA reporting a drug shortage as recent as March 2017.

What Does Promethazine Treat?

Promethazine can relieve symptoms of allergic reactions, when used as an antihistamine.

Promethazine helps relieve the symptoms of allergic reactions such as:
  • Allergic rhinitis (runny nose and watery eyes)
  • Allergic conjunctivitis (red, watery eyes)
  • Allergic skin reactions (rash, hives)
  • Allergic reactions to blood or plasma products

It can also be used in combination with other medications, such as epinephrine, to treat anaphylaxis (a sudden, severe allergic reaction) once the condition is controlled, as well as symptoms of the common cold, such as sneezing, cough and runny nose.

Although primarily used to treat allergies, Promethazine is indicated to treat a variety of other conditions as well.

Promethazine can also be used for the following conditions:
  • Sedation, to calm and to produce a light sleep in patients, before and after surgery, during labor and at other times
  • To prevent and to treat motion sickness
  • To prevent and to control nausea and vomiting associated with certain types of anesthesia and post-surgery
  • In combination with analgesics (painkillers) to help control pain after surgery
  • Intravenously in special surgical situations

How Does Promethazine Work?

Promethazine is used as a histamine-receptor blocker. Histamine receptors are proteins that bind with histamine to produce allergic reactions. This makes promethazine an effective antihistamine. The drug also blocks acetylcholine receptors, making it useful to prevent and treat nausea and morning sickness. Promethazine can only help control symptoms. It isn’t effective in treating the cause of symptoms or in speeding recovery, according to the National Institutes of Health (NIH).

Promethazine Side Effects

Promethazine can cause many different side effects, some common and some serious. These side effects can affect several different body systems and organs including the brain, heart, skin, blood, stomach and intestines and lungs.

The two most serious side effects of the antihistamine medication are addressed in a boxed warning on the drug’s labeling. These reactions include respiratory depression, which can be fatal, occurring primarily in children under the age of 2, and severe tissue damage, including gangrene (a dangerous, potentially fatal condition that involves the loss of blood flow to a large area of tissue, causing it to break down and die), primarily associated injection problems.

Common promethazine side effects:
  • Drowsiness
  • Difficulty falling asleep or staying asleep
  • Nightmares
  • Dizziness
  • Blurred or double vision
  • Vomiting
Serious promethazine side effects:
  • Slowed breathing
  • Fast or irregular pulse or heartbeat
  • Abnormal or uncontrollable movements
  • Hallucinations (seeing things or hearing voices that do not exist)
  • Confusion
  • Overwhelming or unmanageable fear or emotion
  • Seizures
  • Unusual bruising or bleeding
  • Uncontrolled eye movements

Promethazine’s Black Box Warnings

Promethazine hydrochloride-containing products administered by injection contain two black box warnings. This is the most serious type of warning issued by the FDA for drugs and medical devices, meaning that the side effects can cause serious injury and possibly death.

The first black box warning for promethazine was added in late 2004. Promethazine is widely used in children as an antihistamine and a sedative, as well as in the treatment of nausea and vomiting. But serious and even deadly adverse events, including respiratory depression, oversedation, agitation, hallucinations, seizures, and dystonic reactions, have been reported in children, according to the New England Journal of Medicine (NEJM).

Promethazine Black-box Warning Label
Black box warning label for the promethazine drug Phenergan

In 1995, the American Academy of Pediatrics took steps to discourage the use of promethazine in combination with other drugs and as an anesthetic premedication in children. But it wasn’t enough, as told by NEJM, and in 2000, the warnings section of the label was strengthened to recommend that promethazine not be used in children younger than 2, and that it be used with caution in older children. But despite the labeling efforts, the FDA continued to receive adverse event reports, some about fatal respiratory depression in young children.

A 2004 review of serious adverse event reports submitted to the FDA between 1969 and 2003, showed a total of 125 patients with 38 cases of respiratory depression or cardiac arrest, as published by NEJM.

Of those 38 cases, 22 involved patients aged 18 months to 2 years of age, and 7 resulted in death. Serious outcomes, including death, disability, life-threatening events, and hospitalization, occurred with all routes of administration, whether oral, rectal or intravenous injection.

“The unpredictable nature of adverse events and their serious outcomes justified further strengthening of warnings and contraindications and the addition of a boxed warning for the use of promethazine in children.”

The New England Journal of Medicine

The black box warning now clearly reads that promethazine hydrochloride injections should not be used in pediatric patients less than 2 years of age because of the potential for fatal respiratory depression. It also advises caution should be exercised when administering the drug in the form of an injection to patients 2 and older.

In 2006, an FDA alert advised all health care professionals that the warning extended to promethazine hydrochloride (including brand name Phenergan and generic versions of the drug) in any form, whether syrups, suppositories, tablets or injectables.

Promethazine’s Gangrene Risk

In 2009, the FDA required a second black box warning for promethazine hydrochloride injection to warn patients of the risks of severe tissue injury, including gangrene, associated with the administration of the drug.

Did You Know
The FDA advised manufacturers to include in the black box warning that the preferred route of intravenous administration is directly into a muscle.

The FDA advised manufacturers to include in the black box warning that the preferred route of intravenous administration is deep intramuscular injection (directly into a muscle) and not subcutaneous injection (into the layer of skin directly below the dermis and epidermis).

Purple Drank

The misuse of a liquid combination of promethazine hydrochloride and codeine (a narcotic pain reliever), indicated to treat common cold symptoms and cough, has become “increasingly popular among youth in several areas of the country,” according to the National Institute on Drug Abuse.

The prescription cough syrup has been known to sell on the streets for upwards of $1,000, with one brand (that the company stopped distributing in 2014) selling for as much as $3,000, Bloomberg said in 2017.

Purple cough syrup in spoon
The prescription cough syrup is also known as “purple drank”

“It’s the caviar of drugs,” said Ronald Peters, a retired professor of behavioral sciences at the University of Texas Health Science Center in Houston.

It was reported that promethazine codeine syrup was prescribed about 4 million times in the U.S. in 2016, bringing in about $15 million in sales. Where it’s selling on the streets, the popular syrup is known as “purple drank,” or simply “drank.”

The U.S. Department of Health and Human Services reported that 11,000 emergency room visits occurred in the United States in 2011 (the most recent year for which data is available) as the result of codeine misuse. But even with the FDA newly scrutinizing codeine since 2013, and requiring adjusted drug labeling warnings about risks to children, the agency has not yet addressed the dangers associated with recreational use of promethazine codeine syrups, according to Bloomberg.

According to one press officer for the FDA, Sarah Peddicord, “The agency is currently evaluating all available information (latest safety data) to determine whether additional communication and/or regulatory action is needed.”

How Is Promethazine Administered?

Promethazine can be administered by mouth in tablet or syrup (liquid) form, by injection (intravenously), or into the rectum in the form of a suppository. When taking liquid promethazine, patients should use a measuring spoon or cup made specifically for measuring medications, and not a household spoon. The suppository can only be inserted through the rectum (lower part of the large intestine through the anus), and should not be swallowed.

Prior to removing the wrapper, if a suppository feels soft, the patient should first hold under cold, running water for one minute. After removing the wrapper, the tip of the suppository should be dipped in water prior to insertion, using the finger. In adults, the suppository should be inserted into the rectum by one inch and by about one-half to one inch in children 2 and older.

Intramuscular Injection
Deep intramuscular injection is the preferred method of promethazine injection

Since promethazine HCI administered intravenously (by injection) can cause severe chemical irritation and damage to tissues, deep intramuscular injection (a technique administering medication deep into the muscles) is the preferred method of injection. Promethazine hydrochloride injections should not be given by intra-arterial (within an artery) injection, under any circumstances, due to the risk of severe arteriospasm (spasm in an artery) and resulting gangrene.

Subcutaneous (the layer of skin directly below the dermis and epidermis – true skin) injection is also not advised as it may result in tissue necrosis (death of a body tissue when there is not enough blood flow to the tissue).

Promethazine Dosages

Dosing for patients taking promethazine may vary based on the condition being treated, a patient’s age and weight, other medications that a patient may be taking and other medical conditions that they may have.

Dosages by Condition:
Allergic Conditions
Average adult dose is 25 milligrams; may repeat at the same dose within two hours, if needed; continued therapy (if needed) should be administered by the oral route.
In hospitalized adults, 25 to 50 milligrams of promethazine hydrochloride injection is recommended to achieve nighttime sedation.
Nausea and Vomiting
The usual adult dose is 112.5 to 25 milligrams, to be given no more than every four hours.
Before and After Surgery
To be used in combination with pre- and post-surgery medication at a dose of 25 to 50 milligrams of promethazine hydrochloride injection in adults; not recommended for children less than two years of age.
In doses of 50 milligrams to provide sedation and promote relaxation in the early stages of labor; when labor is established, dosing can be 25 to 75 milligrams (with the average dose at 50 milligrams) when given with a reduced dose of another painkiller; may be repeated once or twice in four-hour intervals with the maximum total dose not to exceed 100 milligrams of promethazine hydrochloride injection within a 24-hour period.
Pediatric Patients
Promethazine hydrochloride injections should not be used in children less than 2 years of age; caution should be used when given to older children with the lowest effective dose recommended; the dose should not exceed half that of the suggested adult dose.
When Administered Intravenously
A dose no greater than 25 milligrams per milliliter and at a rate not to exceed 25 milligrams per minute.

Promethazine & Drug Interactions

Promethazine can potentially interact with a number of other medications. Taking promethazine with certain medications can decrease the effectiveness of either drug or increase a patient’s risk of unwanted side effects.

Medicines and other substances that may interact with promethazine include:
  • Alcohol
  • Acetycholinesterase inhibitor medications – used to treat dementia in patients with Alzheimer’s disease
  • Anticholinergic drugs – used to treat a variety of conditions including dizziness, gastrointestinal disorders, insomnia (short-term), respiratory disorders and sinus bradycardia (a heart beat that is regular but slower than normal)
  • CYP 2B6 inhibitor medications, such as Paxil and Zoloft
  • CYP 2D6 inhibitor medications, such as Chlorpromazine, Prozac, Miconazole, Paxil, Quinidine and Ritonavir (Norvir)
  • Epinephrine (adrenaline) – a hormone, neurotransmitter (messenger in the brain) and medication
  • Monoamine Oxidase Inhibitors (MAOIs) – used for the treatment of depression
  • Pramlintide (Symlin) – used to treat diabetes by lowering blood sugar levels
Other medications that can cause drowsiness, such as:
  • Antipsychotic medications
  • Anxiety medications
  • Most antidepressants
  • Muscle relaxants
  • Narcotic pain relievers
  • Sleep medications
  • Some antihistamines

Please seek the advice of a medical professional before making health care decisions.

Kristin Compton
Written By Kristin Compton Writer

Kristin Compton's background is in legal studies. She worked as a paralegal before joining Drugwatch as a writer and researcher. She was also a member of the National Association of Legal Assistants. A mother and longtime patient, she has firsthand experience of the harmful effects prescription drugs can have on women and their children. Some of her qualifications include:

  • Bachelor of Arts in Legal Studies | Pre-Law from University of West Florida
  • Past employment with The Health Law Firm and Kerrigan, Estess, Rankin, McLeod & Thompson LLC
  • Personal experience battling severe food allergies, asthma and high-risk pregnancies
Edited By
Kevin Connolly
Kevin Connolly Managing Editor

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  5. FDA. (16 September 2009). Information for Healthcare Professionals: Intravenous Promethazine and Severe Tissue Injury, Including Gangrene. Retrieved from:
  6. FDA. (23 March 2017). FDA Drug Shortages: Promethazine (Phenergan) Injection. Retrieved from:
  7. MedlinePlus, NIH. (15 June 2017). Promethazine. Retrieved from:
  8. NEJM. (23 June 2005). Boxed Warning Added to Promethazine Labeling for Pediatric Use. Retrieved from:
  9. University of Bristol. (27 July 2017). Histamine receptors. Retrieved from:
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