Clemastine (Tavegyl)

What Is Clemastine and What Is It Used For?

Clemastine belongs to the ethanolamine class of first-generation antihistamines. It works by competitively and reversibly blocking histamine H1 receptors on effector cells in the gastrointestinal tract, blood vessels, respiratory tract, and skin. When histamine is released during an allergic reaction, it binds to these receptors and triggers symptoms such as itching, swelling, increased mucus production, and redness. By occupying these receptor sites, clemastine prevents histamine from exerting its effects, thereby reducing or eliminating allergic symptoms.

Histamine is one of the primary chemical mediators released by mast cells and basophils during allergic responses. It is involved in many types of allergic reactions, including immediate hypersensitivity reactions (Type I). When an individual who has been previously sensitized to an allergen encounters that substance again, their immune system triggers a cascade of events that leads to the release of histamine and other inflammatory mediators. Clemastine intervenes in this process by blocking the downstream effects of histamine on H1 receptors.

As a first-generation antihistamine, clemastine readily crosses the blood-brain barrier, which accounts for its sedative properties. This characteristic distinguishes it from newer, second-generation antihistamines such as cetirizine and loratadine, which are designed to have reduced central nervous system penetration. While the sedation caused by clemastine is generally considered a side effect, in some clinical contexts — such as when itching is causing significant sleep disturbance — this property may actually be beneficial.

Clemastine also possesses anticholinergic (antimuscarinic) properties, which contribute to some of its therapeutic effects as well as certain side effects. The anticholinergic action helps reduce secretions and can be useful in managing the runny nose associated with allergic rhinitis. However, it can also lead to dry mouth, urinary retention, and constipation, particularly in susceptible individuals.

Approved Indications

Clemastine is approved for the treatment of the following conditions:

• Urticaria (hives) — Red, itchy welts on the skin caused by allergic reactions, including both acute and chronic forms.
• Allergic rhinitis (hay fever) — Seasonal or perennial nasal inflammation triggered by allergens such as pollen, dust mites, or animal dander.
• Insect bite and sting reactions — Local allergic reactions to bites and stings from insects such as bees, wasps, mosquitoes, and other arthropods.
• Angioedema — Allergic swelling of deeper layers of skin, often affecting the face, lips, tongue, or throat.
• Pruritus (itching) — Clemastine has a general anti-itch effect and is used for various types of itching, particularly those associated with allergic skin conditions and dermatitis.

After oral administration, clemastine is well absorbed from the gastrointestinal tract. The onset of action typically occurs within 1 to 2 hours, with peak plasma concentrations reached within 2 to 5 hours. The duration of action is approximately 10 to 12 hours, allowing for twice-daily dosing. Clemastine is extensively metabolized in the liver and its metabolites are primarily excreted through the kidneys in the urine.

What Should You Know Before Taking Clemastine?

Before starting clemastine treatment, it is important to discuss your complete medical history with your prescribing physician. Several medical conditions may affect the safety and appropriateness of clemastine therapy. Your doctor will assess whether the benefits of treatment outweigh the potential risks in your individual case. Being fully transparent about your health conditions and other medications is essential for safe and effective use.

Contraindications

You should not take clemastine if:

• You are allergic (hypersensitive) to clemastine, other antihistamines of the ethanolamine class, or any of the inactive ingredients in the formulation (including lactose monohydrate, povidone, magnesium stearate, talc, and maize starch).
• The patient is a child under 1 year of age. Clemastine is contraindicated in infants due to the risk of central nervous system depression and potential interference with normal development.

Warnings and Precautions

Speak with your doctor before taking clemastine if you have any of the following conditions, as special monitoring or dose adjustments may be required:

• Seizure disorders (epilepsy) — Antihistamines can lower the seizure threshold and may increase the risk of convulsions in susceptible individuals. Your physician may need to adjust your antiepileptic medication.
• Narrow-angle glaucoma — The anticholinergic effects of clemastine can increase intraocular pressure, which may worsen glaucoma. Regular eye pressure monitoring may be advisable.
• Severe gastrointestinal disease — Including peptic ulcer disease and pyloroduodenal obstruction. Clemastine’s anticholinergic properties may reduce gastric motility and delay gastric emptying.
• Prostatic hyperplasia (enlarged prostate) — The anticholinergic effects can worsen urinary retention symptoms in men with benign prostatic hyperplasia.
• Bladder neck obstruction — Any condition that causes urinary outflow obstruction may be exacerbated by clemastine’s anticholinergic effects.
• Myasthenia gravis — This autoimmune neuromuscular disorder may be worsened by the anticholinergic actions of clemastine, potentially impairing muscle function further.
• Porphyria — A group of metabolic disorders that may be affected by clemastine. Patients with porphyria should use this medication with caution and under close medical supervision.

Dry mouth and dental health: Clemastine may cause dry mouth (xerostomia) in some patients. Good oral hygiene is particularly important during long-term treatment because reduced saliva production increases the risk of dental caries and oral infections. Consider using saliva substitutes or sugar-free chewing gum to help stimulate saliva flow.

Contact lens wearers: Reduced tear production due to the anticholinergic effects of clemastine may cause problems for contact lens wearers. If you experience eye dryness or discomfort, consider using lubricating eye drops and discuss alternatives with your ophthalmologist.

Pregnancy and Breastfeeding

If you are pregnant, breastfeeding, think you may be pregnant, or are planning to have a baby, consult your doctor or pharmacist before taking clemastine. The safety of clemastine during pregnancy has not been fully established in controlled human studies. Animal reproductive studies are not always predictive of human response, so clemastine should only be used during pregnancy when the physician determines that the potential benefit justifies the potential risk to the fetus.

Clemastine is known to pass into breast milk. Because of the potential for adverse reactions in nursing infants — particularly drowsiness and irritability — breastfeeding mothers should either discontinue clemastine or discontinue breastfeeding, based on the importance of the medication to the mother. Second-generation antihistamines such as cetirizine or loratadine are generally preferred during pregnancy and breastfeeding due to their better safety profile.

Driving and Operating Machinery

Like other first-generation antihistamines, clemastine can significantly impair psychomotor performance, reaction time, and cognitive function. You should not drive motor vehicles, operate heavy machinery, or perform tasks that require mental alertness until you understand how clemastine affects you personally. These effects can be particularly pronounced at the start of treatment and when the dose is increased. Combining clemastine with alcohol or other central nervous system depressants greatly amplifies the impairment.

Lactose Content

Clemastine tablets contain lactose monohydrate as an inactive ingredient. If you have been diagnosed with a lactose intolerance or a rare hereditary condition of galactose intolerance, the Lapp lactase deficiency, or glucose-galactose malabsorption, consult your doctor before taking this medicine.

How Does Clemastine Interact with Other Drugs?

Drug interactions can alter how clemastine works or increase your risk of serious side effects. As a first-generation antihistamine with sedative and anticholinergic properties, clemastine has the potential to interact with a wide range of medications. Keep a comprehensive list of all prescription drugs, over-the-counter medicines, vitamins, and herbal supplements you use, and share it with every healthcare provider you see. Never start, stop, or change the dose of any medication without consulting your doctor.

Major Interactions

The following interactions are clinically significant and may require dose adjustments, close monitoring, or avoidance of concomitant use:

Minor Interactions

The following interactions are generally manageable but should be considered during treatment:

Food Interactions

Clemastine should be taken before meals for optimal absorption and effectiveness. Food does not significantly reduce the total amount of drug absorbed, but taking it on an empty stomach allows for faster onset of action. Grapefruit juice has not been shown to significantly affect clemastine metabolism, but it is generally advisable to take medications with water rather than juice to ensure consistent absorption.

What Is the Correct Dosage of Clemastine?

Always take clemastine exactly as your doctor has prescribed. Do not change your dose or stop taking the medication without consulting your healthcare provider first. The dosage may vary depending on the severity of your condition, your age, and other individual factors. If you are uncertain about any aspect of your dosing schedule, ask your doctor or pharmacist for clarification.

Adults

Children

Elderly

Dosage Summary Table

Missed Dose

If you forget to take a dose, take it as soon as you remember, provided it is not close to the time of your next scheduled dose. If it is nearly time for the next dose, skip the missed one and continue with your regular dosing schedule. Do not take a double dose to make up for a forgotten tablet, as this increases the risk of side effects including excessive drowsiness and anticholinergic toxicity.

Overdose

If you have taken more clemastine than prescribed, or if a child has accidentally ingested the medication, contact your doctor, hospital emergency department, or poison control center immediately. Overdose with first-generation antihistamines can be serious, particularly in children. Symptoms of overdose may include:

• Extreme drowsiness progressing to deep sedation or coma
• Paradoxical excitation, agitation, and hallucinations (especially in children)
• Seizures (convulsions)
• Dilated pupils (mydriasis) and blurred vision
• Dry mouth and flushed, hot skin
• Rapid heartbeat (tachycardia) and cardiac arrhythmias
• Urinary retention
• In severe cases, respiratory depression and cardiovascular collapse

Treatment of overdose is primarily supportive, with gastric lavage and activated charcoal if the patient presents within one hour of ingestion. There is no specific antidote for clemastine overdose, although physostigmine may be used in severe cases of anticholinergic toxicity under specialist guidance.

What Are the Side Effects of Clemastine?

Like all medicines, clemastine can cause side effects, although not everyone experiences them. Most side effects are mild to moderate and tend to diminish as your body adjusts to the medication over the first few days of treatment. However, some side effects can be serious and require immediate medical attention. Understanding the frequency and nature of possible side effects helps you make informed decisions about your treatment and know when to seek medical advice.

Managing Common Side Effects

Drowsiness, the most frequently experienced side effect, often improves after a few days of regular use as tolerance develops. Taking the evening dose at bedtime can help minimize daytime sedation. If drowsiness is persistent and disruptive, talk to your doctor about lowering the dose or switching to a less-sedating antihistamine such as cetirizine, loratadine, or fexofenadine.

For dry mouth, maintain good oral hygiene including regular brushing and flossing, stay well hydrated, and consider sugar-free lozenges or chewing gum to stimulate saliva production. If you experience dizziness, rise slowly from sitting or lying positions to minimize the effect. Constipation can usually be managed by increasing dietary fiber and fluid intake.

Reporting Side Effects

Reporting suspected side effects after a medicine has been authorized is important. It allows ongoing monitoring of the medicine’s benefit-risk balance. Healthcare professionals and patients are encouraged to report any suspected adverse reactions through their national pharmacovigilance system, such as the FDA MedWatch program in the United States, the Yellow Card Scheme in the United Kingdom, or the EMA EudraVigilance system in the European Union.

How Should You Store Clemastine?

Proper storage of medications is essential to maintain their effectiveness and safety. Clemastine tablets should be stored in the original blister packaging at room temperature, typically below 25°C (77°F). Protect the tablets from direct sunlight, excessive heat, and moisture, as these environmental factors can degrade the active ingredient and reduce the medication’s efficacy.

Keep clemastine out of the sight and reach of children at all times. Consider using a lockable medicine cabinet for added safety, particularly in households with young children. Accidental ingestion of antihistamines by children can lead to serious adverse effects and requires immediate medical attention.

Do not use clemastine after the expiration date (marked as “EXP” on the packaging). The expiration date refers to the last day of the indicated month. Expired medications may not provide adequate therapeutic effect and could potentially contain degradation products.

Do not dispose of unused or expired medicines via household waste or by flushing them down the toilet. Return unused medications to your local pharmacy for safe disposal. Proper disposal of medicines helps protect the environment from pharmaceutical contamination, which can affect water systems and aquatic ecosystems.

What Does Clemastine Contain?

Understanding the complete composition of your medication is important, particularly if you have known allergies to specific excipients (inactive ingredients) or if you have conditions such as lactose intolerance that may be affected by the tablet’s formulation.

Active Ingredient

Each tablet contains 1 mg of clemastine (equivalent to 1.34 mg of clemastine hydrogen fumarate). Clemastine is the pharmacologically active component responsible for the antihistaminic effects. The fumarate salt form is used to improve the stability and bioavailability of the active substance.

Inactive Ingredients (Excipients)

• Lactose monohydrate — A filler (diluent) that makes up the bulk of the tablet. Patients with lactose intolerance should discuss this with their doctor.
• Povidone — A binding agent that holds the tablet ingredients together.
• Magnesium stearate — A lubricant that prevents the tablet from sticking to manufacturing equipment during production.
• Talc — A flow agent and lubricant used in tablet manufacturing.
• Maize starch — A disintegrant that helps the tablet break down after swallowing for proper absorption.

Tablet Appearance

Clemastine 1 mg tablets are white, round, uncoated tablets. They measure 7 mm in diameter and are marked with “OT” on one side. The tablets have a score line to allow splitting into halves, which facilitates accurate dosing for children and elderly patients. The tablets also feature beveled edges for easier handling and swallowing.

Available Pack Sizes

Clemastine tablets are available in blister packs containing 20, 60, 80, 98×1, or 100 tablets, as well as bottles containing 500 tablets (for institutional or pharmacy use). Not all pack sizes may be marketed in every country. The most commonly available package for patients is the 20-tablet or 60-tablet blister pack.

References

This article is based on the following authoritative medical sources. All information has been reviewed according to the GRADE evidence framework with evidence level 1A.

1. World Health Organization (WHO). WHO Model List of Essential Medicines – 23rd List. Geneva: WHO; 2023. Available at: who.int
2. European Medicines Agency (EMA). Clemastine – Summary of Product Characteristics. Amsterdam: EMA. Available at: ema.europa.eu
3. British National Formulary (BNF). Clemastine. London: BMJ Group and Pharmaceutical Press; 2025. Available at: bnf.nice.org.uk
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5. Church MK, Maurer M, Simons FER, et al. “Risk of first-generation H1-antihistamines: a GA2LEN position paper.” Allergy. 2010;65(4):459–466. DOI: 10.1111/j.1398-9995.2009.02325.x
6. American Geriatrics Society 2023 Beers Criteria Update Expert Panel. “American Geriatrics Society 2023 Updated AGS Beers Criteria.” Journal of the American Geriatrics Society. 2023;71(7):2052–2081. DOI: 10.1111/jgs.18372
7. Zuberbier T, Abdul Latiff AH, Abuzakouk M, et al. “The international EAACI/GA²LEN/EuroGuiDerm/APAAACI guideline for the definition, classification, diagnosis, and management of urticaria.” Allergy. 2022;77(3):734–766. DOI: 10.1111/all.15090
8. U.S. Food and Drug Administration (FDA). Clemastine Fumarate – Prescribing Information. Silver Spring, MD: FDA. Available at: fda.gov

Editorial Team

This article has been written and medically reviewed by iMedic’s editorial team of specialist physicians in clinical pharmacology and allergy. All medical content follows international guidelines and the GRADE evidence framework.

Evidence standard: Level 1A — Based on systematic reviews and meta-analyses of randomized controlled trials. No commercial funding or pharmaceutical sponsorship.