What Is Clemastine Fumarate?

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  • Written By: wiseGEEK Writer
  • Edited By: Jessica Seminara
  • Last Modified Date: 04 November 2019
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Clemastine fumarate is a medication that is principally used in the treatment of hay fever type allergies. It is available in over-the-counter and prescription strength forms, and is also sometimes recommended or prescribed to treat itching or hives. Though the drug can cause some sedation, it may cause less sleepiness or drowsiness than a few other common antihistamines. This may make clemastine a good choice for treatment, but patients should understand its side effects, drug interactions, and contraindications before they use it.

An antihistamine blocks histamine response that occurs in the presence of allergy-causing substances like pollen. Clemastine fumarate also has anticholinergic properties that assist in drying excess nasal excretions. In addition, the medication is an antipruritic, which means it can aid in the treatment of itching or hives. A comparable medication like diphenhydramine also has antihistamine and anti-itch effects, but clemastine fumarate may be preferred because it is less sedating for some patients.

There are different strengths of clemastine fumarate available. Low dose pills are often sold without a prescription. These may have a variety of brand names. Stronger doses, containing up to 2.68 milligrams (mg) of the drug, can be obtained with a prescription. Severe hives or persistent allergies might be best treated with larger doses, but physicians generally recommend the lowest effective dose to minimize side effects.


The most common adverse effect of clemastine fumarate is dry mouth. Some people will feel sedation or dizziness when they use this medication, and this may be most apparent in the first few days of taking the drug. Others notice an increase in bronchial secretions and wheezing. Additional side effects include stomach upset and poor coordination.

More concerning side effects are trouble breathing, a fast heart rate, reduced urination, and ringing in the ears. Some patients have what is called a paradoxical reaction to the drug and become extremely hyperactive or agitated when they take it. Serious changes to mood may occur for a small percentage of individuals who use clemastine fumarate. In rare cases, the drug may cause seizures or extreme allergic reaction. If any of these dangerous side effects occur, patients need immediate medical attention.

Some patients shouldn’t use clemastine fumarate or are advised to talk to a doctor prior to obtaining it. The medication’s safety isn’t established in pregnant or nursing women, or in children under the age of 12, who are especially likely to have paradoxical reactions to the drug. It’s recommended that patients with asthma, prostate enlargement, or glaucoma avoid clemastine because it can worsen these illnesses. High blood pressure, liver disease, and hyperthyroidism contraindicate the drug’s use, too.

Clemastine fumarate may interact with many other drugs. Any medications that have sedating properties, like benzodiazepines, opioids, antipsychotics, and barbiturates, may increase the sedative effects of clemastine. As a general rule, patients should discuss all other medications, including herbal and vitamin supplements, with a doctor or pharmacist before they begin use of a new drug.


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