Desentol

What Is Desentol and What Is It Used For?

Desentol is an oral solution containing diphenhydramine hydrochloride (3.72 mg/mL), a first-generation antihistamine used to treat allergic reactions such as hives (urticaria), hay fever (allergic rhinitis), and allergic itching. It also contains ammonium chloride, which has a mild expectorant effect to help loosen mucus.

Diphenhydramine, the active ingredient in Desentol, belongs to the ethanolamine class of first-generation H1 antihistamines. It was one of the earliest antihistamines to be developed and has been used in clinical practice since the 1940s. Despite the availability of newer, non-sedating antihistamines, diphenhydramine remains widely used due to its proven efficacy in managing acute allergic symptoms and its additional pharmacological properties, including anticholinergic and sedative effects.

The primary mechanism of action involves competitive blockade of histamine H1 receptors. When the body encounters an allergen – such as pollen, insect venom, or certain foods – mast cells and basophils release histamine, which binds to H1 receptors throughout the body. This binding triggers the classic symptoms of allergic reactions: itching, swelling, redness, runny nose, and watery eyes. By occupying these receptors, diphenhydramine prevents histamine from exerting its effects, thereby alleviating allergic symptoms.

In addition to its antihistamine properties, diphenhydramine has significant anticholinergic (antimuscarinic) activity. This means it blocks the neurotransmitter acetylcholine at muscarinic receptors, which contributes to some of its therapeutic effects (such as drying nasal secretions) but also accounts for many of its side effects, including dry mouth, urinary retention, and constipation. The anticholinergic properties should be taken seriously, particularly in elderly patients and those with certain pre-existing conditions.

Desentol also contains ammonium chloride as an additional active component. Ammonium chloride acts as a mild expectorant by stimulating mucus secretion in the airways, making it easier to cough up phlegm. This combination makes Desentol particularly useful in patients who experience both allergic symptoms and upper respiratory congestion, as it addresses both the histamine-mediated allergic response and mucus accumulation.

The sedative properties of diphenhydramine are well-documented and result from the drug’s ability to cross the blood–brain barrier and block H1 receptors in the central nervous system. While this sedation can be considered a side effect in patients who need to remain alert, it can be therapeutically useful for patients whose allergic symptoms are disrupting sleep. According to the World Health Organization’s Model List of Essential Medicines, antihistamines remain an important therapeutic class for the management of allergic conditions worldwide.

What Should You Know Before Taking Desentol?

Before taking Desentol, inform your doctor about all your medical conditions, especially glaucoma, urinary difficulties, prostate enlargement, or myasthenia gravis. Desentol must not be used in infants under 1 year or together with tricyclic antidepressants and anticholinergic medications.

Contraindications

You should not take Desentol if any of the following apply to you:

• Allergy to diphenhydramine hydrochloride or any other ingredient in Desentol – symptoms of an allergic reaction may include skin rash, itching, swelling of the face or throat, or difficulty breathing
• Raised pressure in the eye (glaucoma) – diphenhydramine’s anticholinergic effects can increase intraocular pressure, potentially worsening glaucoma and risking permanent vision damage
• Concurrent use with tricyclic antidepressants (such as amitriptyline, nortriptyline, or imipramine) – the combined anticholinergic effects can lead to serious adverse reactions including severe dry mouth, urinary retention, constipation, confusion, and cardiac arrhythmias
• Concurrent use with anticholinergic (atropine-like) medications – combining these drugs can dangerously amplify anticholinergic side effects throughout the body
• Infants under 1 year of age – first-generation antihistamines may cause paradoxical excitation, respiratory depression, and other serious adverse effects in very young infants

Warnings and Precautions

Talk to your doctor or pharmacist before taking Desentol if you have any of the following conditions, as the medication may need to be used with particular caution or at an adjusted dose:

• Urinary tract narrowing or obstruction – the anticholinergic properties of diphenhydramine can worsen urinary retention, making it difficult or impossible to urinate
• Enlarged prostate (benign prostatic hyperplasia) – men with this condition are at particular risk of acute urinary retention when taking anticholinergic medications
• Pyloric stenosis (narrowing of the lower stomach outlet) – anticholinergic effects can slow gastric emptying, exacerbating symptoms of obstruction
• Myasthenia gravis (a condition causing severe muscle weakness) – anticholinergic drugs may interfere with neuromuscular transmission and worsen muscle weakness
• Impaired liver or kidney function – diphenhydramine is metabolised by the liver and its metabolites are excreted by the kidneys; reduced organ function can lead to drug accumulation and increased risk of toxicity

Desentol can cause dry mouth with regular use. Saliva plays an important protective role for dental health, and chronic dry mouth significantly increases the risk of tooth decay, gum disease, and oral infections. Patients who use Desentol regularly should brush their teeth with fluoride toothpaste at least twice daily and consider using saliva substitutes or sugar-free chewing gum to stimulate saliva production.

Desentol can also cause dry eyes with regular use. Contact lens wearers should be particularly cautious, as reduced tear production can lead to corneal abrasion and damage. If you wear contact lenses and notice eye dryness, discomfort, or redness, consult your eye care professional promptly.

Pregnancy and Breastfeeding

If you are pregnant or breastfeeding, think you may be pregnant, or are planning to have a baby, ask your doctor or pharmacist for advice before using Desentol.

Pregnancy: No adverse effects on the foetus have been demonstrated in available studies. However, as a precautionary measure, Desentol should only be used during pregnancy when the expected benefit to the mother outweighs any potential risk to the unborn child. The American College of Obstetricians and Gynecologists (ACOG) notes that diphenhydramine is generally considered acceptable for short-term use during pregnancy when antihistamine treatment is required, but patients should always consult their healthcare provider before taking any medication during pregnancy.

Breastfeeding: Diphenhydramine passes into breast milk. Due to the potential for sedation and anticholinergic effects in the nursing infant, Desentol should not be used during breastfeeding. If antihistamine treatment is needed while breastfeeding, your doctor may recommend a non-sedating second-generation antihistamine that has a more favourable safety profile during lactation.

Driving and Operating Machinery

Desentol can cause significant drowsiness, dizziness, blurred vision, and impaired coordination. You are responsible for assessing whether you are fit to drive a motor vehicle or perform work that requires alertness. Do not drive, operate heavy machinery, or engage in potentially hazardous activities until you know how Desentol affects you. The sedative effects of diphenhydramine can persist for several hours after a dose and may be more pronounced when treatment is first started or when the dose is increased.

How Does Desentol Interact with Other Drugs?

Desentol can interact with a number of other medications, including certain heart medicines, antidepressants, and sedatives. The most important interactions involve drugs that have anticholinergic properties or central nervous system depressant effects, as these can be dangerously amplified.

Drug interactions involving diphenhydramine can be clinically significant and, in some cases, dangerous. Diphenhydramine is metabolised primarily by the liver through the cytochrome P450 enzyme system, particularly CYP2D6. This means it can both affect and be affected by other drugs that use the same metabolic pathways. Additionally, its anticholinergic and sedative properties can be additive with those of other medications.

Always tell your doctor or pharmacist about all medicines you are currently taking, have recently taken, or might take, including over-the-counter products, herbal remedies, and dietary supplements. The following table summarises the most important known drug interactions with Desentol:

Major Interactions

Other Important Interactions

The interaction between diphenhydramine and CYP2D6 substrates is particularly noteworthy. Diphenhydramine is a moderately potent inhibitor of this enzyme, which is responsible for metabolising many commonly prescribed medications. When diphenhydramine inhibits CYP2D6, co-administered drugs that are metabolised by this enzyme may accumulate in the body, reaching higher blood levels than intended. This can increase the risk of dose-dependent side effects of those medications. Patients who are already taking medications metabolised by CYP2D6 should discuss potential interactions with their healthcare provider before starting Desentol.

What Is the Correct Dosage of Desentol?

Desentol dosing is individualised by a physician based on the patient’s age and weight. The usual adult dose is 10 mL (37.2 mg diphenhydramine) taken 2–4 times daily. Children’s doses are calculated by weight and age, ranging from 1 mL to 5 mL per dose depending on the child’s size.

Always use Desentol exactly as your doctor or pharmacist has told you. If you are unsure about the correct dose, ask your doctor or pharmacist for clarification. The dose is determined by the prescribing physician and is individually tailored based on age, body weight, and the severity of symptoms. The liquid formulation makes it particularly convenient for precise dose adjustments, especially in paediatric patients.

Adults

Children

Desentol dosing for children is carefully calculated based on both age and body weight. A physician must determine the appropriate dose for each individual child. The following table provides the standard recommended dosing guidelines:

It is essential that parents and caregivers use an accurate measuring device (such as an oral syringe or graduated medicine cup) to measure the dose. Household teaspoons and tablespoons are not accurate enough for measuring liquid medications and should not be used. If you are unsure about how to measure the dose correctly, ask your pharmacist for a suitable measuring device and instructions on how to use it.

Elderly Patients

Elderly patients may be more sensitive to the effects of diphenhydramine, particularly its anticholinergic and sedative properties. The American Geriatrics Society Beers Criteria lists first-generation antihistamines, including diphenhydramine, as potentially inappropriate medications for older adults due to the increased risk of confusion, sedation, falls, urinary retention, and constipation. If Desentol is prescribed for an elderly patient, the lowest effective dose should be used, and the patient should be carefully monitored for adverse effects. Alternative non-sedating antihistamines should be considered as first-line treatment whenever possible.

Missed Dose

If you forget to take a dose of Desentol, take it as soon as you remember. However, if it is nearly time for your next scheduled dose, skip the missed dose entirely and continue with your regular dosing schedule. Do not take a double dose to make up for a forgotten dose, as this increases the risk of side effects, particularly excessive drowsiness and anticholinergic adverse effects.

Overdose

Diphenhydramine overdose can cause a range of serious and potentially life-threatening symptoms. In mild to moderate overdose, patients may experience extreme drowsiness, dilated pupils, dry mouth, flushed skin, and rapid heartbeat. In severe overdose, symptoms can progress to seizures, hallucinations, delirium, cardiac arrhythmias, respiratory depression, and coma. Children are particularly vulnerable to overdose toxicity and may develop seizures more readily than adults. Treatment is supportive and symptomatic, and may include gastric lavage, activated charcoal, and monitoring in an intensive care setting.

What Are the Side Effects of Desentol?

Like all medicines, Desentol can cause side effects, although not everybody gets them. The most common side effects are drowsiness and dry mouth. More serious but less frequent side effects include cardiac arrhythmias, severe confusion, and urinary retention.

The side effects of Desentol are largely attributable to the pharmacological properties of diphenhydramine, specifically its antihistaminic, anticholinergic, and CNS-depressant activities. The frequency and severity of side effects vary between individuals and are generally dose-dependent. Side effects tend to be more pronounced when treatment is first started and may diminish over time as the body develops some tolerance to the sedative effects. However, anticholinergic effects generally do not diminish with continued use.

The following is a categorised list of known side effects, organised by frequency of occurrence:

The sedative effects of diphenhydramine deserve particular attention. Unlike newer, non-sedating antihistamines such as cetirizine, loratadine, or fexofenadine, diphenhydramine readily crosses the blood–brain barrier and binds to central H1 receptors. This central action is responsible for the significant drowsiness that many patients experience. Studies have shown that even a single dose of diphenhydramine can impair psychomotor performance and cognitive function for several hours, comparable to moderate alcohol intoxication. Patients should be explicitly warned about this effect, especially during the initial days of treatment.

The anticholinergic side effects of diphenhydramine are an important consideration, particularly for certain patient groups. Dry mouth, constipation, urinary retention, and blurred vision are all direct consequences of muscarinic receptor blockade. In elderly patients, the anticholinergic burden of diphenhydramine can contribute to cognitive impairment, an increased risk of falls, and delirium. The Anticholinergic Cognitive Burden Scale classifies diphenhydramine as having a “definite” anticholinergic burden, the highest category.

Cardiac effects, while uncommon at therapeutic doses, can occur particularly in cases of overdose or when diphenhydramine is combined with other drugs that affect cardiac conduction. Diphenhydramine has sodium channel blocking properties similar to class Ia antiarrhythmic drugs, which can prolong the QRS interval and potentially lead to ventricular tachycardia or other arrhythmias at high doses. Patients with pre-existing cardiac conditions should use Desentol with caution and under close medical supervision.

How Should You Store Desentol?

Store Desentol out of the sight and reach of children. Do not use after the expiry date printed on the bottle. Store at room temperature and protect from excessive heat and light.

Proper storage of medications is essential to ensure they remain effective and safe to use. Desentol should be kept in its original brown glass bottle, which protects the solution from light degradation. Store the bottle at room temperature, typically between 15°C and 25°C (59°F to 77°F). Do not store it in the bathroom or near a sink where it may be exposed to moisture, and do not freeze the solution.

Keep Desentol out of the sight and reach of children at all times. Accidental ingestion of diphenhydramine by young children can cause serious harm and requires immediate medical attention. Consider storing the bottle in a locked medicine cabinet or on a high shelf that children cannot access.

Do not use Desentol after the expiry date (marked “EXP”) printed on the bottle. The expiry date refers to the last day of the stated month. Expired medications should be disposed of safely – do not throw them in the rubbish bin or flush them down the toilet, as this can contaminate the environment. Instead, return unused or expired medicines to your local pharmacy for safe disposal.

Before each use, visually inspect the solution. Desentol should be a clear, colourless to slightly yellowish solution. If the liquid appears cloudy, discoloured, or contains visible particles, do not use it and contact your pharmacist for advice.

What Does Desentol Contain?

The active substance in Desentol is diphenhydramine hydrochloride at a concentration of 3.72 mg/mL. The solution also contains ammonium chloride as a mild expectorant, along with various inactive excipients.

Active Substance

Each millilitre of Desentol oral solution contains 3.72 mg of diphenhydramine hydrochloride. Diphenhydramine hydrochloride is the salt form of diphenhydramine, which improves the drug’s water solubility and allows it to be formulated as a liquid preparation. Diphenhydramine itself is an ethanolamine derivative that functions as a competitive antagonist at histamine H1 receptors.

Other Ingredients (Excipients)

In addition to the active substance, Desentol contains the following excipients, each serving a specific purpose in the formulation:

• Ammonium chloride – acts as a mild expectorant to help loosen mucus in the airways
• Macrogolglycerol hydroxystearate – an emulsifier that helps mix the ingredients evenly in solution
• Sodium citrate – acts as a buffer to maintain the appropriate pH of the solution
• Citric acid – works with sodium citrate as part of the buffering system
• Sorbitol – a sweetener and humectant (426 mg per mL); a source of fructose
• Saccharin sodium – an artificial sweetener to improve palatability
• Liquorice essence – a flavouring agent
• Anise oil – a flavouring agent
• Purified water – the solvent base of the solution

Physical Description

Desentol is supplied as a clear, colourless to slightly yellowish solution in a 250 mL brown glass bottle. The brown glass provides protection from light, which could otherwise degrade the active ingredient over time. The bottle should be shaken gently before use if any settling has occurred.

Frequently Asked Questions About Desentol

References and Sources

This article is based on the latest international medical guidelines and peer-reviewed scientific literature. All medical claims are supported by Level 1A evidence where applicable.

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Editorial Team

This article was written and reviewed by the iMedic Medical Editorial Team, consisting of licensed specialist physicians with expertise in allergy, immunology, and clinical pharmacology.