Compazine vs Phenergan

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For patients who experience severe nausea or vomiting, certain medications that alter the activity of neurotransmitters in the brain can help manage these symptoms. Compazine and Phenergan are two such drugs that are often prescribed for these conditions. They each impact different pathways in the brain but both have antiemetic effects, helping to control nausea and vomiting. Compazine is a phenothiazine derivative, which works by blocking postsynaptic mesolimbic dopaminergic D1 receptors in the brain, thus reducing feelings of sickness. On the other hand, Phenergan (promethazine), is classified as a first-generation antihistamine with strong sedative properties; it primarily affects histamine H1 receptors but also has some effect on muscarinic receptors and alpha-adrenergic receptors.

What is Compazine?

Prochlorperazine (the generic name for Compazine) and Promethazine (known as Phenergan) are both part of the phenothiazine class of antiemetic drugs, which marked a significant advancement from previous medications used to treat nausea and vomiting. Prochlorperazine was first approved by the FDA in 1956. Compazine works by blocking dopamine receptors in the brain, effectively reducing feelings of nausea and the urge to vomit. It is prescribed for various conditions that cause nausea or vomiting, such as chemotherapy or surgery. Compared to Promethazine, Prochlorperazine has a more selective influence on dopamine receptors with only minor effects on other neurotransmitters like histamine and acetylcholine; this results in fewer side effects than other antiemetics that have stronger effects on these two other neurotransmitters.

What conditions is Compazine approved to treat?

Compazine is approved for the treatment of certain conditions:

  • Severe nausea and vomiting
  • Psychotic disorders such as schizophrenia
  • Non-psychotic anxiety

Phenergan, on the other hand, is indicated for:

  • Allergy symptoms such as rash, itching, and runny nose
  • Preoperative sedation
  • Nausea or vomiting related to surgery or chemotherapy
  • Certain types of joint pain and swelling.

How does Compazine help with these illnesses?

Compazine helps to manage nausea and vomiting by blocking the effects of dopamine in the brain. Dopamine is a neurotransmitter, a chemical that acts as a messenger in the brain and throughout the body, that plays an important role in mood, cognition, reward-seeking behavior, movement regulation amongst other things. In certain parts of the brain like chemoreceptor trigger zone (CTZ), it leads to feelings of nausea and triggers vomiting reflexes. By blocking dopamine receptors specifically within these areas such as CTZ, Compazine can limit episodes of nausea and vomiting thereby offering relief to patients undergoing treatments which induce these symptoms or suffering from conditions causing them.

On the other hand Phenergan also helps manage similar symptoms but its mechanism differs slightly - it works predominantly by blocking histamine receptors. Histamine has multiple roles inside our bodies including triggering allergic reactions but when present in excess at specific places like part of our brains called vestibular system, it can cause motion sickness leading to nausea & vomiting. Hence by inhibiting this histaminergic pathway within our central nervous systems Phenergan too alleviates these distressing symptoms aiding patients.

What is Phenergan?

Phenergan, the brand name for promethazine, is a first-generation antihistamine that inhibits the action of histamine in your body by reducing its production. It also has strong sedative properties and can be used as a preoperative sedative or to treat insomnia. Phenergan was approved by the FDA in 1951 and remains a popular choice due to its effectiveness against allergy symptoms.

The medication functions differently from Compazine; it doesn’t have significant effects on dopamine receptors which means it's less likely to cause extrapyramidal side effects (movement disorders). However, because of its sedating properties, drowsiness is one common side effect along with dry mouth and dizziness. The benefits provided by Phenergan can be particularly useful for patients suffering from severe allergies or requiring pre-surgery calming.

What conditions is Phenergan approved to treat?

Phenergan has been given the green light by FDA for managing and treating:

  • Allergy symptoms, such as rash, itching, and runny nose
  • Preoperative sedation to calm or sedate a patient before surgery
  • Nausea and vomiting related to certain conditions (such as after surgery or in patients undergoing cancer treatment)
  • Motion sickness

How does Phenergan help with these illnesses?

Histamine is a compound which acts as a neurotransmitter, playing significant roles in local immune responses and acting as a mediator of itching. In addition, it also has important roles in the brain where it helps to regulate sleep-wake cycles. Phenergan works by blocking the effects of histamine produced by the body making it highly effective at relieving allergy symptoms such as hay fever, rashes, and hives. Furthermore, its sedative properties can help with insomnia and are often utilized for preoperative sedation or to treat motion sickness. It functions differently from Compazine which primarily targets dopamine receptors to control severe nausea and vomiting. Therefore, if patients do not respond well to typical antiemetics like Compazine or need additional relief from allergies or insomnia, Phenergan may be prescribed.

How effective are both Compazine and Phenergan?

Both prochlorperazine (Compazine) and promethazine (Phenergan) have established histories of success in treating nausea and vomiting, as well as other conditions, with their initial FDA approvals taking place decades ago. Both are classified as phenothiazines and function by blocking certain chemicals in the brain that trigger nausea and vomiting.

A 2012 clinical trial demonstrated comparable efficacy between prochlorperazine and promethazine for emergency department patients presenting with vertigo, however, it was noted that drowsiness occurred more frequently in those receiving promethazine.[1] Earlier studies also showed similar effectiveness between these two drugs for postoperative nausea control.[2]

[1] [2]

While both medications have been shown to be effective antiemetics, their side effect profiles differ somewhat. Prochlorperazine may cause extrapyramidal symptoms such as tremor or involuntary muscle movements more commonly than Promethazine -- a factor which can influence prescribing decisions based on individual patient characteristics.

Interestingly enough, while traditionally used primarily for their antiemetic properties, Compazine is also sometimes employed off-label to treat anxiety disorders due to its calming effects - a use not typically associated with Phenergan.

Overall though there's substantial evidence supporting the efficacy of both prochlorperazin and promethazin in managing symptoms of various conditions including queasiness induced by anesthesia or chemotherapy. The choice between them often depends on specific patient factors like potential drug interactions or sensitivity to particular side effects.

abstract image of a researcher studying a bottle of drug.

At what dose is Compazine typically prescribed?

Oral dosages of Compazine range from 5-10 mg, three to four times per day for adults. However, studies have shown that an initial dosage of 5 mg is often adequate for controlling nausea and vomiting in most people. For children aged between two and twelve years old, the starting dose should be calculated based on their weight: approximately 2.5-5 mg but not exceeding a maximum daily dose of 20mg. In both populations, if there's no response after a few days, the dosage can be increased up to the recommended maximum limit which should not exceed more than 40mg/day for adults or as advised by a healthcare professional.

At what dose is Phenergan typically prescribed?

Phenergan treatment typically begins with a dose of 12.5 to 25 mg taken orally or rectally before bedtime or prior to surgery procedures. This dosage may then be increased, depending on the response and tolerance of the patient, but should not exceed a maximum daily dose of 75mg. The medication can also be divided into multiple doses throughout the day if needed for nausea and vomiting control. For example, one could take three doses evenly spaced out over a period of time recommended by your healthcare provider. If no significant improvement is seen after using Phenergan at this rate for a few weeks, it's important to consult with your healthcare professional for further guidance.

What are the most common side effects for Compazine?

Common side effects of Compazine (Prochlorperazine) include:

  • Drowsiness, dizziness
  • Amenorrhea (absence of menstruation)
  • Nasal congestion
  • Blurred vision
  • Skin rash, itching
  • Dry mouth
  • Weight gain or weight loss

While common side effects for Phenergan (Promethazine) are:

  • Drowsiness, somnolence
  • Tinnitus (ringing in the ears)
  • Incoordination, trembling
  • Euphoria (feeling intense excitement and happiness) -Dry mouth
    -Angioneurotic edema(swelling in the lower layer of skin and tissue just under the skin or mucous membranes) -Tachycardia(fast heart rate)

Always consult with your healthcare provider if you experience any of these symptoms while taking these medications.

abstract image of a patient experiencing side effect

Are there any potential serious side effects for Compazine?

Compazine and Phenergan are both effective medications, but they carry potential side effects. With Compazine, rare yet serious side effects may include:

  • Allergic reactions such as hives, difficulty breathing, swelling of your face or throat
  • Severe nervous system reaction - symptoms can include stiff muscles, high fever, sweating, confusion and uneven heartbeats
  • Uncontrolled muscle movements in your face (chewing, lip smacking etc.), tongue or other body parts
  • Symptoms associated with low levels of sodium in the body – headache, confusion slurred speech severe weakness vomiting loss of coordination feeling unsteady.

Alternatively with Phenergan some serious but unlikely side effects could include:

  • Mental/mood changes such as hallucinations or extreme excitement
  • Abnormal heartbeat rhythm evidenced by a fast or slow heart rate
  • Involuntary behaviors like eye movements/blinkings/twitching/restlessness/pacing/tongue movement

If you experience any these symptoms while taking either medication please consult with your healthcare provider immediately.

What are the most common side effects for Phenergan?

With Phenergan, you may experience some side effects such as:

  • Dry mouth
  • Drowsiness or fatigue
  • Blurred vision
  • Constipation
  • Occasional dizziness
  • Feeling restless or agitated
  • Skin rash or itching
  • Potential weight gain due to increased appetite
  • Difficulty urinating.

Though not common, it's also possible to experience tremors, uncontrolled muscle movements, and confusion. As always with medication use, if any of these symptoms persist or worsen, please consult your healthcare provider promptly.

Are there any potential serious side effects for Phenergan?

While Phenergan is commonly used and generally safe, it can in rare instances cause serious side effects. Be on the lookout for:

  • Signs of an allergic reaction such as hives, difficulty breathing or swelling in your face, lips, tongue or throat.
  • Little to no urination or painful urination.
  • Uncontrolled movements of your eyes, tongue, jaw or neck.
  • Hallucinations (seeing things that don't exist), agitation and nightmares.
  • Jaundice (yellowing of your skin or eyes).
  • Severe dizziness leading to fainting spells,
  • Slow heart rate with weak pulse; or
  • Nosebleeds/bloody gums.

If you experience any of these symptoms while taking Phenergan, stop immediately and seek medical attention.

Contraindications for Compazine and Phenergan?

Both Compazine and Phenergan, as with many other antiemetic medications, may exacerbate symptoms in some people. If you notice an increase in restlessness, confusion or unusual behavior after taking these drugs, please seek immediate medical attention.

Neither Compazine nor Phenergan should be taken if you are also using large amounts of alcohol or medicines that cause drowsiness. Always tell your physician which substances you are consuming; this will help to avoid dangerous interactions with both Compazine and Phenergan.

It's important to remember that elderly patients particularly those suffering from dementia-related psychosis treated with antipsychotic drugs like compazine are at an increased risk of death. The use of these drugs is not approved for the treatment of patients with dementia-related psychosis.

Also keep in mind when comparing these two medications that they have different side effects profiles: While phenergan might lead to dry mouth and constipation among others, compazine can result in more serious neurological side effects such as tardive dyskinesia (a syndrome consisting of potentially irreversible involuntary movements). Therefore it is essential to discuss any potential risks associated with medication use during a consultation.

How much do Compazine and Phenergan cost?

For the brand name versions of these drugs:

  • The price of 60 tablets of Compazine (10 mg) averages around $250-$300, which works out to approximately $4–5/day, depending on your dose.
  • The price of 30 tablets of Phenergan (25 mg) averages about $100-$150, working out to roughly $3.33–$5/day.

Should you be in a higher dosage range for Compazine (i.e., 20 mg/day or more), then brand-name Phenergan may be less expensive per day treatment basis. Keep in mind though that cost should not be the primary consideration when deciding which medication is best suited for you.

As with most medications, generic versions are considerably cheaper:

  • Prochlorperazine (generic version of Compazine) is available in packs starting from 30 tablets and above, with approximate costs ranging from $0.15 to $0.50 per day if dosages are at typical levels between 15 and 20mg/day.
  • Promethazine (the generic form of Phenergan) comes in packages varying from as few as a dozen capsules up to several hundred. For this drug too prices can start from just a few cents per day ($0.03 if buying larger quantities upfront), but typically do not exceed about $1 per day even for smaller quantity purchases.

Popularity of Compazine and Phenergan

Prochlorperazine, sold under brand names such as Compazine, was estimated to have been prescribed to roughly 1.2 million people in the US in 2020. Prochlorperazine accounted for just over 10% of prescriptions among antiemetic medications (drugs that help control nausea and vomiting). It is most commonly used as a short-term treatment for severe nausea and vomiting from any cause.

Promethazine, also known by its brand name Phenergan, was prescribed to around 4.8 million people in the USA during the same year. Promethazine accounts for just under 30% of overall antiemetic prescriptions. Similar to prochlorperazine, it's primarily used for preventing motion sickness and treating allergy symptoms like runny nose or watery eyes.

While both these drugs are very effective at controlling nausea and vomiting when taken correctly, they each possess their own unique side effects which should be considered before usage. The prevalence of promethazine has been approximately steady over the last decade while prochlorperzaine has seen a slight decrease during this time frame.


Both Compazine (prochlorperazine) and Phenergan (promethazine) have long-standing records of usage in patients for the treatment of nausea, vomiting, motion sickness, and allergies. Both drugs are backed by numerous clinical studies indicating their effectiveness above placebo treatments. In some cases, these drugs may be combined but this would require careful consideration by a physician as they can interact with each other. Due to their different mechanisms of action - Compazine acting primarily on dopamine receptors while Phenergan acts on histamine receptors - they tend to be prescribed under different circumstances.

Both drugs are available in generic form which represents significant cost savings especially for patients who must pay out of pocket. Both Compazine and Phenergan may require an adjustment period as effects may not be noticeable right away.

The side effect profile is similar between the two drugs; both being generally well-tolerated but can cause drowsiness or sedation. For both medications, patients should monitor themselves closely when starting treatment and seek medical help immediately if they notice any severe reactions such as difficulty breathing or signs of infection like fever or persistent sore throat.