Allersoothe

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Medically reviewed

Marina Burgos

Last updated on 22/12/2025

This page provides general, reference-level information compiled from official medical sources. It is not a substitute for professional medical advice, diagnosis, or treatment. For decisions about your health, please consult a qualified healthcare professional.

Overview of Allersoothe

Property Description
Active ingredient Promethazine hydrochloride
Forms Tablet, syrup, injection, suppository
Pharmacological class First-generation antihistamine
Common purpose Relief of allergic symptoms and sedation
Origin Synthetic compound

What is Allersoothe and Its Pharmacological Class?

Allersoothe is a specific trade name utilized in various markets for the synthetic compound Promethazine hydrochloride, which is fundamentally classified as a potent first-generation antihistamine and a phenothiazine derivative. This drug primarily acts as an H₁-receptor antagonist, blocking the effects of histamine released during allergic responses. The unique chemical structure of Promethazine is clinically recognized for enabling the drug to easily penetrate the central nervous system (CNS), a differentiating factor from later-generation antihistamines. This means the medicine is scientifically recognized for both relieving hypersensitivity reactions and promoting a calming effect.

Composition and Available Forms of Promethazine

The medicine is supplied as a single active ingredient product, containing only Promethazine as the therapeutic component. To ensure effective systemic delivery across various situations, Allersoothe is notably available in multiple dosage forms, including the standard oral tablet and syrup (oral solution). Importantly, its availability as a sterile parenteral solution for injection and as a suppository makes it a versatile choice for patients, such as those experiencing severe episodes of vomiting where oral intake is compromised. This broad range of forms is a key feature of its use across acute care and standard outpatient settings.

The General Purpose of This First-Generation Antihistamine

The primary therapeutic utility of Promethazine is derived from its dual pharmacological functions: effective histamine antagonism and strong influence on the CNS. By counteracting histamine, the drug provides comprehensive relief for general allergic reactions, including pruritus and rhinitis. Moreover, its established capacity for inducing CNS depression makes it beneficial for providing short-term sedation or sleep facilitation. This dual utility confirms the medicine's role in addressing symptoms related to motion sickness and gastric distress.

Regulatory References

  1. NIH - Promethazine Fact Sheet

What side effects are possible with Allersoothe?

Possible Side Effects and Safety Information

The safety profile for Promethazine hydrochloride (Allersoothe) details adverse reactions and safety constraints established in government regulatory documents.

Officially Documented Adverse Reactions

The most frequently classified adverse reactions are effects on the Central Nervous System (CNS), which include sedation, drowsiness, dizziness, and impaired mental and physical performance, listed as common in official regulatory documents. Other common effects documented in the gastrointestinal system include dry mouth, nausea, vomiting, and constipation.

Adverse effects are documented across various System-Organ Classes, including the neurological, cardiovascular (e.g., hypotension), and psychiatric systems. Rarer effects reported include blood disorders such as leukopenia and agranulocytosis.


Serious Safety Constraints and Warnings

Official regulatory labeling outlines several serious risks. A primary constraint is the absolute contraindication for use in pediatric patients under two years of age due to the potential for fatal respiratory depression. Older adults are also noted to be more susceptible to the drug's sedative and anticholinergic effects.

For the injection form, there is a serious warning regarding the risk of severe tissue injury, necrosis, or gangrene, regardless of the specific route of administration. Furthermore, the drug is associated with a risk of Neuroleptic Malignant Syndrome (NMS) and a potential for lowering the seizure threshold.


Safety Context

These classifications reflect the regulatory framework used to communicate the risk magnitude (common, rare, etc.). Use is strictly restricted in comatose states and for patients with existing lower respiratory tract symptoms. The CNS depressant effects are emphasized, requiring caution in the initial phase of therapy.

Overdose and Emergency Response

Overdose and When to Seek Help

The official regulatory documents for Allersoothe (Promethazine hydrochloride) define overdose by severe, documented manifestations across the central nervous, cardiovascular, and respiratory systems. Immediate medical attention must be sought if an overdose is suspected, which includes contacting the local Poison Control Center or emergency services. All appropriate measures are mandated to be taken immediately.

Documented Manifestations and Severe Outcomes:

Overdose symptoms may present along a spectrum of neurological changes. This includes profound Central Nervous System (CNS) depression (e.g., marked drowsiness, respiratory depression, or coma), and paradoxically, symptoms of CNS excitation (e.g., agitation, hallucinations, seizures, and involuntary extrapyramidal effects) are also documented, particularly in pediatric patients. Anticholinergic signs, such as tachycardia and urinary retention, may also occur. Cardiovascular complications, such as serious arrhythmias, QTc prolongation, and severe hypotension, are recognized outcomes.

Population-Specific and Management Notes:

Regulatory information highlights a heightened risk for the pediatric population, where excessively large dosages are associated with the potential for sudden death. Treatment is mandated to be symptomatic and supportive, as there is no specific antidote listed in the official prescribing information. A critical constraint is that Epinephrine must not be used to treat associated low blood pressure.

Therapeutic Uses of Allersoothe

What Allersoothe Treats: Main Uses and Benefits

Allersoothe is commonly used across domains where additional symptomatic support is needed, with its therapeutic scope covering symptoms related to systemic imbalance, heightened physiological activity, and the need for short-term rest. This medication generally provides supportive relief when symptoms interfere with routine activities.

The drug is commonly applied in addressing conditions associated with certain distressing symptoms, including allergic manifestations, nausea and vomiting, motion sickness, and the need for short-term rest. It helps address symptom clusters that may become intense or disruptive, such as pruritus (itching), rhinorrhea, vomiting, and acute apprehension. This provides supportive relief when symptoms interfere with routine activities and contributes to improved comfort during periods of heightened symptoms.


Symptom Focus: Relief for Pruritus and Nausea

This medication is commonly used in clinical settings that involve acute or unstable symptom patterns, and assists with managing symptom clusters that may become intense or disruptive. The drug is relevant for managing symptoms that interfere with daily comfort and is used when groups of symptoms appear suddenly or fluctuate.

Eligibility and Restrictions for Use

Who Can and Cannot Use Allersoothe?

The official regulatory profile for Allersoothe (Promethazine) strictly defines eligible populations based on age, pre-existing conditions, and physiological status.

Absolute Contraindications: The medicine is contraindicated for all pediatric patients less than two years of age due to the serious risk of fatal respiratory depression. It must not be used in individuals who are comatose or experiencing severe Central Nervous System (CNS) depression, or those with a documented hypersensitivity to promethazine or related phenothiazine derivatives. Use is also contraindicated for treating lower respiratory tract symptoms.

Age and Condition Restrictions: Oral formulations are not recommended or contraindicated in children under six years of age in many regions due to documented CNS side effects. In adults, use requires caution in the presence of impaired liver function or renal insufficiency. Caution is also warranted for patients with seizure disorders, narrow-angle glaucoma, or prostatic hypertrophy. Older adults also require caution due to increased susceptibility to effects.

Pregnancy and Lactation Status: The medicine is not recommended for individuals who are breastfeeding. Use during pregnancy is officially restricted to only if essential after benefit-risk assessment, and is not recommended in the final two weeks of pregnancy.

What should I know about interactions with other medicines?

Interactions with other medicines and products

The interaction profile for Allersoothe (Promethazine hydrochloride) is formally defined by regulatory authorities based on both pharmacokinetic and pharmacodynamic mechanisms.

Prohibited and High-Risk Combinations

The medicine is strictly contraindicated for co-administration with Monoamine Oxidase Inhibitors (MAOIs), including for 14 days following the cessation of MAOI therapy. A significant risk involves additive central nervous system (CNS) depression when taken with substances such as alcohol, opioid analgesics, sedative hypnotics, or tranquilizers, which may increase the intensity of sedative effects. Concurrent use with other anticholinergic agents will enhance antimuscarinic effects. The combination with drugs known to cause QT interval prolongation is advised against.

Pharmacokinetic and Administration Constraints

Promethazine is officially documented as a moderate inhibitor of the CYP2D6 enzyme, a classification that indicates a potential for increased plasma concentrations of co-administered medicines that are metabolized by this pathway.

  • Timing Separation: Non-absorbed gastrointestinal agents (such as certain antacids containing aluminum or magnesium) should be administered with a separation of at least two hours to prevent reduced absorption.
  • Procedural Constraint: The medicine must be discontinued for 72 hours prior to allergen skin testing to avoid false-negative results.
  • Population Note: Special consideration is noted for elderly patients receiving antihypertensive therapy, due to a heightened potential for hypotension.

Mechanism of Action

Central Nervous System (CNS) Pathway Modulation

This domain is defined by the drug's rapid, extensive penetration across the blood-brain barrier and its antagonism of central Histamine H1 receptors and Muscarinic acetylcholine receptors ( M1). This dual-receptor blockade directly suppresses the activity of the ascending neural systems responsible for wakefulness and arousal, initiating a cascading physiological effect of generalized CNS functional downregulation.


Multitarget Suppression of Emetic Signals

The anti-emetic mechanism is a complex multitarget process that involves the simultaneous antagonistic action on multiple signaling molecules in the brainstem. Specifically, it blocks Dopamine D2 receptors in the Chemoreceptor Trigger Zone (CTZ) and M1 receptors in the Vomiting Center, which prevents neuronal excitation from motion and chemical stimuli. This concerted suppression of key inputs leads to a substantial physiological suppression of the emetic reflex arc.


Peripheral H1 Receptor Blockade

In the peripheral tissues, the drug's primary action is the competitive antagonism of H1 receptors. This mechanism limits the effects of released histamine on the local microvasculature, preventing the excessive dilation and increased permeability of capillaries. This physiological interference with the inflammatory cascade leads to decreased histamine-mediated fluid exudation and sensory nerve stimulation.

Dosage and Administration Information

Official Administration Instructions

Allersoothe (Promethazine hydrochloride) must be administered according to specific methods and dosage patterns. The medication is available for Oral (tablet, syrup), Rectal (suppository), and Parenteral (Deep Intramuscular or cautious Intravenous) use. Subcutaneous injection is explicitly prohibited as a route of administration.

Standard Labeled Dosing Regimens

Administration frequency and dose are strictly defined by the intended use, and effects typically last between four and twelve hours.

Indication Standard Adult Dosing (Typical Range) Frequency / Timing
Allergy Symptoms 25 mg OR 6.25 mg to 12.5 mg Once daily at bedtime OR 3-4 times daily (before meals and at bedtime)
Nausea and Vomiting 12.5 mg to 25 mg Repeated every 4 to 6 hours as needed
Nighttime Sedation 25 mg to 50 mg Single dose at bedtime

Preparation and Special Conditions

  • Oral Intake: Tablets or syrup may be taken with food, water, or milk to help lessen stomach irritation.
  • IV Injection: Intravenous administration is reserved for situations where deep intramuscular injection is not feasible. The injectable solution must be diluted and infused through a large vein at a rate not exceeding 25 mg per minute to mitigate the risk of severe tissue injury.
  • Concomitant Use: Doses of narcotics or barbiturates taken concurrently for sedation must be reduced by one-quarter to one-half.

Age-Based Administration Rules

The medication is contraindicated for administration to children under two years of age. For pediatric patients aged two years and older, dosing is based on the patient's weight and the specific intended use, prioritizing the lowest effective amount.

Recent Clinical Evidence

Allersoothe: Recent Clinical Evidence

Evidence for Core Indications

Research on Allersoothe (Promethazine hydrochloride) is focused on exploring its role in conditions characterized by fluctuating or episodic symptoms, such as allergic rhinitis, itching, nausea, and vomiting. The evidence base includes short-term Randomized Controlled Trials (RCTs) and historical regulatory data.

For allergic manifestations, studies monitored outcomes related to physical discomfort in adults and children aged two years and older. The findings describe patterns related to short-term symptom changes observed following a single dose. Research on nausea and vomiting (including motion sickness and post-operative events) used meta-analyses and RCTs to examine acute episodes, measuring nausea severity and the frequency of vomiting. The compound’s effects on the central nervous system were also evaluated, with outcomes measured by the onset and duration of CNS depressive effects, relevant to temporary rest and sedation.


Evidence Gaps and Limitations

The evidence base for this compound is consistent with its regulatory status, but its focus is primarily on acute, single-dose administration; long-term effects are not fully established across any main indication. Follow-up durations in key studies were limited to hours or short-term protocols. Comparative evidence is lacking when assessing Allersoothe against newer medications that offer different profiles.

Data for specific patient populations and complex health issues remains insufficient. For instance, while children aged two years and older were included, research on long-term chronic use is not well characterized. Subgroup findings in patients with specific comorbid conditions also remain uncertain, highlighting a research gap in these areas.

Frequently Asked Questions (FAQ)

Common questions about Allersoothe (FAQ)


Q: What is the duration of action for a dose of Allersoothe?

Official regulatory information indicates that the duration of effect generally lasts between four and six hours. In some cases, effects may be observed for up to 12 hours. This duration of effect is an established measurement based on official product data.


Q: Do many people experience tiredness or drowsiness with Allersoothe?

Yes, regulatory documents list sedation and drowsiness as the most frequently documented effects of this medication on the central nervous system (CNS). This indicates that tiredness is among the most frequently documented effects.


Q: Does taking Allersoothe with food change how it works?

The official product information states that the oral forms of the medication, such as tablets or syrup, may be taken with food, water, or milk. This is noted as a method to potentially reduce stomach irritation. Regulatory materials do not describe food intake as significantly altering the medication's effectiveness or action.


Q: What should be done if a common side effect is bothersome?

If a common, documented effect—such as tiredness or dizziness—is bothersome, official patient information advises speaking with a pharmacist or healthcare provider. This step allows a healthcare professional to review symptoms and provide general guidance.


Q: Is Allersoothe considered a short-term or long-term medicine?

The primary clinical evidence base for this medicine focuses on acute, short-term relief of symptoms. The follow-up periods in studies are short-term, and some protocols are limited to use for no longer than seven continuous days.


Q: What is the difference between Allersoothe and a typical over-the-counter allergy pill?

Allersoothe's active ingredient, Promethazine, is classified as a first-generation antihistamine. It is scientifically recognized for its ability to easily affect the central nervous system, leading to prominent sedative effects. The strong CNS effect is a notable feature that separates it from some other antihistamines.


Q: Are there any common foods or drinks that should be avoided when taking Allersoothe?

Regulatory documents strongly caution against consuming alcohol while taking this medication. The warning is due to the potential for significant additive central nervous system (CNS) depression. No specific common foods are routinely listed for avoidance.


Q: Is Allersoothe known to cause any long-term health issues?

The official documentation indicates that the evidence base for this compound is centered on acute, short-term use protocols. As a result, the long-term effects of the compound are not fully established across its main approved uses.


Q: How does Allersoothe's mechanism relate to histamine?

The drug is primarily classified as a competitive antagonist of the Histamine H1 receptors. This mechanism of action is described as limiting the physiological effects that naturally released histamine has on various body tissues.


Q: Can Allersoothe impact the results of laboratory blood tests?

Yes, official labeling notes that Promethazine may interfere with certain immunological urine pregnancy tests. This interference can affect the reliability of the test results.


Q: What is the general consensus on Allersoothe's effectiveness based on research?

The research evidence base is described as consistent with its regulatory status. It relies on short-term Randomized Controlled Trials (RCTs) and historical regulatory data that monitored acute symptom changes following a single dose for conditions like allergies and nausea.


Q: Does Allersoothe have any known drug-disease interactions mentioned in the documentation?

Yes, official documentation describes several drug-disease interactions. The official product information notes that use is restricted in the presence of certain existing conditions, such as severe central nervous system depression, liver disease, certain blood or heart disorders, and specific eye or prostate conditions.


Q: What happens if I miss a dose of Allersoothe?

Official patient instructions provide specific guidance for a missed dose. Individuals are advised to review the patient information leaflet or consult a healthcare professional regarding their next dose.


Q: Are there official studies comparing Allersoothe to a placebo?

Yes, the evidence base for this compound includes results from short-term Randomized Controlled Trials (RCTs). This trial type is used to establish efficacy and typically involves comparing the drug's effects against an inactive substance.


Q: Does Allersoothe have a potential for misuse?

The United States Drug Enforcement Administration (DEA) does not classify Promethazine as a scheduled or controlled substance. However, its potential for non-medical use, particularly when combined with other substances, has been examined in medical literature.


Q: Are there alternative formulations (e.g., liquid, injectable) of Allersoothe?

Yes, the active ingredient, Promethazine, is available in multiple dosage forms to ensure effective delivery across various situations. These include standard oral tablets, oral syrup, sterile solutions for injection, and suppositories.


Q: Is it normal to feel a mild headache after starting Allersoothe?

Headache is listed among the common adverse effects documented for this medication in authoritative medical sources. If symptoms are concerning, consulting a healthcare provider is recommended.


Q: Does the package insert include information about kidney function?

Yes, the prescribing information includes warnings and caution for use in patients with existing renal insufficiency (impaired kidney function). This indicates that information regarding kidney function is included in the drug’s official safety profile.


Q: Is the name Allersoothe used in all countries?

Allersoothe is a specific trade name utilized in various markets for the active ingredient Promethazine hydrochloride. This means that the product may be known by different brand names in different countries.

How should Allersoothe be stored and disposed of?

Storage and Disposal Conditions for Allersoothe

Storage of Allersoothe (Promethazine Hydrochloride) must adhere strictly to the conditions specified in official regulatory labeling to ensure product stability and safety.

Mandatory Storage Requirements

Storage Component Official Requirement
Temperature Store at Controlled Room Temperature (20 C to 25 C).
Protection Must be protected from light; the syrup form must be protected from freezing.
Container Keep in a tightly closed container.
Child Safety Store out of the sight and reach of children.

Disposal Instructions

Unused or expired medication must be disposed of according to local requirements. Official regulatory information states that the product must not be disposed of via wastewater or regular household waste. Patients should consult a pharmacist for guidance on discarding medicines no longer required.

Attention! Always consult to a doctor or pharmacist before using pills or medicines.

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