Clemastine, Clemsza

Introduction

Written by Kirstyn Hill, PharmD, MPH
Medically reviewed by Alex Brewer, PharmD, MBA
Updated on November 7, 2023

Clemastine (KLEM as teen) is a generic medication prescribed for the treatment of certain types of allergic conditions. Clemastine belongs to a group of drugs called antihistamines.

The Food and Drug Administration (FDA) has approved clemastine for use in adults and some children to treat:

• allergic rhinitis (hay fever)
• mild allergic skin reactions, such as hives

Common questions about clemastine

Below you’ll find answers to a few commonly asked questions about clemastine.

What brand names are available for clemastine?

The brand-name version of clemastine, called Tavist, is no longer available in the United States.

Clemastine is a generic medication. A generic medication is an identical copy of the active drug in a brand-name medication. (An active drug is the ingredient that makes a medication work.) Generic drugs are believed to be as effective and safe as brand-name drugs. And generic drugs typically cost less than brand-name drugs. For more information on brand-name versus generic drugs, see this article.

Is clemastine available over the counter?

No, clemastine isn’t available over the counter in the United States. Clemastine is only available with a prescription. If you would like to know more about clemastine or over-the-counter medication options for the treatment of allergy symptoms, talk with your doctor or pharmacist.

How does clemastine work? And how long does it take to start working?

Clemastine works by blocking histamine. Histamine is a chemical that causes allergic symptoms, such as a runny nose, sneezing, or itching. By blocking histamine, clemastine helps relieve these allergy symptoms.

Clemastine should begin to work within 2 hours after you take it. The effects of the medication can last from 12–24 hours.

If you’d like to know more about how clemastine works or how long it takes to start working, talk with your doctor or pharmacist.

Uses of clemastine

The Food and Drug Administration (FDA) approves prescription drugs such as clemastine for certain conditions. Approved uses for clemastine are described below.

Use for allergy symptoms

Doctors may prescribe clemastine for treating allergy symptoms. The oral syrup is used for this purpose in adults and children ages 6 years and older. The oral tablet is used for this purpose in adults and children ages 12 years and older. It’s usually prescribed as a short-term treatment.

Specifically, clemastine is used to treat allergic rhinitis (hay fever) and mild allergic skin reactions, such as hives.

With allergies, your immune system reacts to a typically harmless substance known as an allergen (such as dust, mold, pollen, or some types of food). This can trigger your immune system to release a chemical called histamine. When histamine is released, it may cause symptoms such as sneezing, runny nose, itchy eyes, or skin rash.

Side effects of clemastine

Clemastine may cause mild or serious side effects. More common mild side effects of clemastine and its serious side effects are listed below. This article doesn’t include all possible side effects of the drug. Side effects can vary based on your age, overall health, and any other medications you take.

To learn more about clemastine’s side effects, ask your doctor or pharmacist. You can also refer to the prescribing information for clemastine listed in the “Resources” section.

Mild side effects

More common mild side effects reported with some forms of clemastine are listed below.

This article doesn’t include all possible mild side effects of the drug. To learn more about clemastine’s side effects, refer to the prescribing information for clemastine listed in the “Resources” section.

With many drugs, mild side effects may go away within a few days or a couple of weeks. If the side effects are bothersome, tell your doctor or pharmacist. They may be able to suggest ways to manage them.

Clemastine oral tablet’s and oral syrup’s mild side effects include:

• drowsiness
• thickening of mucus in the lungs
• dizziness
• abdominal pain
• mild allergic reaction*

* For details about this side effect, see the “Interactions and warnings for clemastine” section.

Serious side effects

Serious side effects of clemastine are listed below.

This article doesn’t include all possible serious side effects of the drug. To learn more about clemastine’s side effects, refer to the prescribing information for clemastine listed in the “Resources” section.

With many drugs, serious side effects are possible but not common. If you have serious side effects from this drug, call your doctor right away. If you’re having severe symptoms or a medical emergency, call 911 or a local emergency number.

In general, clemastine’s serious side effects include: 

• low blood pressure
• atypical heart rate
• seizure
• low platelet count
• low neutrophil levels
• severe allergic reaction*

* For details about this side effect, see the “Interactions and warnings for clemastine” section.

Interactions and warnings for clemastine

Below, you’ll find information about clemastine’s possible interactions and warnings.

Interactions of clemastine

Certain things may affect how a drug works. These include getting vaccines, consuming alcohol or certain foods, or taking the drug with other medications. This effect is called a drug interaction.

Before you take clemastine, ask your doctor to check for possible interactions. Be sure to tell them about any of the following you take or use:

• prescription or over-the-counter drugs
• vitamins, herbs, or supplements

To learn about drug-condition interactions, see the “Warnings for clemastine” section below.

Warnings for clemastine

Some people should not take clemastine, and others should take it cautiously.

Clemastine could cause harm to people with certain health conditions. This effect is called a drug-condition interaction. Other factors can also affect whether clemastine is a safe option for you. These warnings may differ based on the form of clemastine you take.

Ask your doctor about specific warnings for clemastine, and be sure to tell your doctor about your:

• current health, including any allergies to medications
• past health conditions or surgeries

Allergic reaction

Clemastine can cause an allergic reaction in some people. Severe allergic reactions are rare but possible.

Although this drug is used to treat certain allergic conditions, clemastine can also cause an allergic reaction in some people.

If you’ve had an allergic reaction to clemastine or any of its ingredients, your doctor will likely not prescribe clemastine. They can tell you about medications that are safer options for you.

A mild allergic reaction may cause the following symptoms:

• skin rash
• itchiness
• flushing (temporary warmth, redness, or deepening of skin color)

A severe allergic reaction may cause the following symptoms:

• swelling under your skin, usually in your hands, feet, eyelids, or lips
• swelling of your mouth, throat, or tongue, which can cause difficulty breathing

If you have an allergic reaction to clemastine, call your doctor right away. If you have severe symptoms, call 911 or a local emergency number.

Overdose of clemastine

You should not take more clemastine than your doctor prescribes. For some drugs, doing so may lead to harmful effects or overdose.

If you think you’ve taken too much clemastine, call your doctor or pharmacist right away. Or you could call 800-222-1222 to speak with someone at America’s Poison Centers. You can also use its online resource. If you have concerning symptoms, call 911 or a local emergency number immediately. You can also go to the closest emergency room.

Pregnancy or breastfeeding and clemastine

Information about clemastine and pregnancy and breastfeeding is described below.

Clemastine and pregnancy

It’s not known whether clemastine should be taken during pregnancy. If you’re planning a pregnancy or can become pregnant, talk with your doctor before taking this medication.

Clemastine and breastfeeding

It’s not known whether clemastine should be taken while breastfeeding. If you’re currently breastfeeding or planning to do so, talk with your doctor before taking this medication.

What to ask your doctor

Let your doctor know if you have questions about clemastine or would like more details about it.

Here’s a list of some possible questions you may want to ask your doctor:

• Am I at a higher risk of side effects from clemastine than others?
• What are my options if I can’t afford clemastine?
• Can I take clemastine with other allergy medications?

Resources

• Clemastine fumarate syrup. (2023). https://nctr-crs.fda.gov/fdalabel/services/spl/set-ids/6663f1b0-5353-401f-b9d3-d9f69ad08fbf/spl-doc
• Clemastine fumarate tablet. (2022). https://nctr-crs.fda.gov/fdalabel/services/spl/set-ids/14aaadca-7d86-47e8-8483-6e05d456949d/spl-doc
• Food and Drug Administration. (2023). Orange Book: Approved drug products with therapeutic equivalence evaluations. https://www.accessdata.fda.gov/scripts/cder/ob/index.cfm

Disclaimer: Optum Perks has made every effort to make certain that all information is factually correct, comprehensive, and up to date. However, this article should not be used as a substitute for the knowledge and expertise of a licensed healthcare professional. You should always consult your doctor or another healthcare professional before taking any medication. The drug information contained herein is subject to change and is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. The absence of warnings or other information for a given drug does not indicate that the drug or drug combination is safe, effective, or appropriate for all patients or all specific uses.