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Overview: Clemastine is an antihistamine that is taken to reduce allergy symptoms. Common side effects may include drowsiness, dizziness, and stomach upset. Do not drive or do other activities that require alertness, coordination, or clear vision until you know how clemastine affects you. Call your health care provider right away if you are having trouble peeing or cannot empty your bladder while taking clemastine.

Uses

What is clemastine used for?

Clemastine is commonly used to relieve allergy symptoms, including nasal, eye, and skin reactions.

Clemastine may also be used for other conditions as determined by your health care provider.

How does clemastine work (mechanism of action)?

Clemastine is an antihistamine. It works by blocking the effect of a substance in your body called histamine.

How is clemastine supplied (dosage forms)?

Brands and other names

  • Dayhist
  • Tavist

Dosage forms and strengths

  • 0.5 mg/5 mL oral syrup
  • 2.68 mg oral tablets

How should I store clemastine?

Clemastine should be stored at room temperature, between 68 F and 77 F (20 C and 25 C). It can be exposed to temperatures between 59 F and 86 F (15 C and 30 C) for shorter periods of time, such as when you’re transporting it. Store it in a cool, dry place.

Side Effects

What are the most common side effects of clemastine?

The most common side effects of clemastine are listed below. Tell your health care provider if you have any of these side effects that bother you.

  • Drowsiness or tiredness
  • Dizziness or feeling off balance
  • Stomach upset
  • Increase in thickness of mucus in the lungs

There may be other side effects of clemastine that are not listed here. Contact your health care provider if you think you are having a side effect of a medicine. In the U.S., you can report side effects to the FDA at www.fda.gov/medwatch or by calling 800-FDA-1088 (800-332-1088). In Canada, you can report side effects to Health Canada at www.health.gc.ca/medeffect or by calling 866-234-2345.

What are the serious side effects of clemastine?

While less common, the most serious side effects of clemastine are described below, along with what to do if they happen.

Severe Allergic Reactions. Clemastine may cause allergic reactions, which can be serious. Stop taking clemastine and get help right away if you have any of the following symptoms of a serious allergic reaction.

  • Breathing problems or wheezing
  • Racing heart
  • Fever or general ill feeling
  • Swollen lymph nodes
  • Swelling of the face, lips, mouth, tongue, or throat
  • Trouble swallowing or throat tightness
  • Itching, skin rash, or pale red bumps on the skin called hives
  • Nausea or vomiting
  • Dizziness, feeling lightheaded, or fainting
  • Stomach cramps
  • Joint pain

Seizures. Some people who have taken clemastine have reported having convulsions, also known as seizures. This may be more common in children. There are many types of seizures, and some of them are not easy to recognize. Stop taking clemastine and call your health care provider if you have any of the following signs that a seizure is happening or could happen.

  • Muscle twitching, jerking, spasms, tremors, or other uncontrolled movements
  • Stiffening of your arms and legs
  • Feeling anxious, nervous, confused, or a sense of dread
  • Feeling dizzy or lightheaded
  • Falling or losing consciousness

Decreased Alertness or Coordination. Clemastine can affect your alertness or coordination. It can also cause blurry vision. Do not drive or do other activities that require alertness, coordination, or clear vision until you know how clemastine affects you.

Inability to Empty Bladder (Urinary Retention). Clemastine might make it harder to empty your bladder, especially if you already have a blockage. Stop taking clemastine and call your health care provider right away if you are having trouble peeing or cannot empty your bladder.

Warnings & Precautions

Who should not use clemastine?

Allergies to Ingredients. People who are allergic to any of the following should not take clemastine.

Your pharmacist can tell you all of the ingredients in the specific clemastine products they stock.

Infants. Clemastine should not be used in newborn or premature babies. This medicine can cause serious side effects in these infants. 

Breastfeeding. Do not take clemastine if you are breastfeeding. You must either stop breastfeeding or stop clemastine. See the Breastfeeding subsection below for more details.

Certain Lung Symptoms. Clemastine should not be taken to treat symptoms of certain lung problems, including asthma.

Drug Interactions. Clemastine should not be taken while you are using certain other medicines. Before taking clemastine, tell your health care provider about any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using. See the Interactions section for more details.

What should I know about clemastine before using it?

Do not take clemastine unless it has been prescribed to you by a health care provider. Take it as prescribed.

Do not share clemastine with other people, even if they have the same condition as you. It may harm them.

Keep clemastine out of the reach of children.

If you are taking clemastine liquid, use an accurate measuring device to measure your dose. A household spoon is not an accurate measuring device and may cause you to take the wrong dose. Ask your pharmacist what measuring device to use.

Clemastine can make your skin more sensitive to light from the sun, sunlamps, and tanning beds. This is called photosensitivity. Exposure to this light can cause severe sunburns, blisters, and swelling. If you need to be in sunlight, wear sunscreen, a hat, and clothing that covers your skin.

People who are 60 and older can be at greater risk of some side effects from clemastine. Talk to your health care provider about your risks if you are in this age group.

What should I tell my health care provider before using clemastine?

Tell your health care provider about all of your health conditions and any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using. This will help them know if clemastine is right for you.

In particular, make sure that you discuss any of the following.

Current and Past Health Conditions. Tell your health care provider if you have any of the following.

  • Increased pressure in your eyes or glaucoma
  • Stomach or bowel problems, including ulcers or blockages
  • Bladder or prostate problems, including a blockage or an enlarged prostate
  • Breathing or lung problems, including asthma
  • Thyroid problems 
  • Heart disease
  • High blood pressure

Pregnancy. It is not known if or how clemastine could affect pregnancy or harm an unborn baby. Tell your health care provider if you are pregnant or plan to become pregnant. Your health care provider will let you know if you should take clemastine while you are pregnant or trying to get pregnant.

Breastfeeding. Do not take clemastine while you are breastfeeding. Clemastine can pass into breast milk. Tell your health care provider if you are breastfeeding or plan to breastfeed.

Interactions

Does clemastine interact with foods or drinks?

There are no known interactions between clemastine and foods or drinks.

Do not drink alcohol while you are taking clemastine. The risk of dizziness and drowsiness may be increased if you drink alcohol while taking clemastine.

Does clemastine interact with other medicines (drug interactions)?

Always tell your health care provider about any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using.

 In particular, make sure that you discuss if you are using any of the following before taking clemastine.

  • A monoamine oxidase inhibitor (MAOI) within the past two weeks, which is a medicine usually used for depression or Parkinson’s disease
  • A barbiturate, such as butalbital, phenobarbital, or primidone, which is a medicine that may be used to treat insomnia, migraines, or seizures
  • A tricyclic antidepressant, such as amitriptyline, nortriptyline, or protriptyline, even if it is not used for depression
  • Any other medicine that causes dizziness and sleepiness, such as prescription pain medicines, other allergy medicines, sleep medicines, or medicines for anxiety 

This may not be a complete list of medicines that can interact with clemastine. Always check with your health care provider.

Does interact with other drugs you are taking?

Enter your medication into the WebMD interaction checker

Overdose/Missed Dose

What should I do if I accidentally use too much clemastine?

If you or someone else has taken too much clemastine, get medical help right away, call 911, or contact a Poison Control center at 800-222-1222.

What should I do if I miss a dose of clemastine?

If you miss a dose, take it as soon as you remember. If it is almost time for your next dose, skip the missed dose and only take the next dose. Do not take double or extra doses.