Antihistamines

Oral antihistamines are available without a prescription. Two types, diphenhydramine hydrochloride (for example, Benadryl) and chlorpheniramine maleate (for example, Chlor-Trimeton), are used to treat allergy symptoms and itching.

Look for generic or store brands, which often cost less than name brands. For example, diphenhydramine is the generic name for the brand name Benadryl.

Antihistamines that are taken by mouth (oral) work better than those that are applied directly to the skin (topical) because a pill or capsule contains a specific dose of medicine. The dose in a cream or ointment depends on how much is applied at one time and is harder to control. Too much antihistamine absorbed through the skin can be toxic, especially to children. Don't give any antihistamines to your child unless you've checked with the doctor first. The use of cream or ointment antihistamines is not reliable and not recommended.

Be sure to follow the nonprescription medicine precautions.

Do not take oral antihistamines when you are driving, operating machinery, or need to be alert because they can make you sleepy.

Use caution if you have other health problems, such as glaucoma, epilepsy, or an enlarged prostate. Antihistamines can cause your other health problem to get worse and also may interact with other medicines, such as antidepressants, sedatives, and tranquilizers. Read the package carefully, and ask your pharmacist or health professional to help you choose an antihistamine that will not cause problems.

Diphenhydramine (Benadryl)

Dosage: 3 or 4 doses in 24 hours.

Adults and children who weigh more than 100 lb (45 kg): 50 mg per dose.

Children who weigh less than 100 lb (45 kg): Doses are based on the child's weight.

Diphenhydramine dose for your child's weight
Child's weight Dose

30 lb (14 kg)

15 mg

40 lb (18 kg)

20 mg

50 lb (23 kg)

25 mg

60 lb (27 kg)

30 mg

70 lb (32 kg)

35 mg

80 lb (36 kg)

40 mg

90 lb (41 kg)

45 mg

Chlorpheniramine (Chlor-Trimeton)

Dosage: 3 or 4 doses in 24 hours.

Adults (age 13 and older): Usually 2 mg to 4 mg per dose. Maximum adult dose is 24 mg in a 24-hour period.

Children: Doses are based on the child's age.

Chlorpheniramine dose for your child's age
Child's age Dose

4 to 5 years old

1 mg per dose. Maximum dose is 4 mg in a 24-hour period.

6 to 12 years old

2 mg per dose. Maximum dose is 8 mg in a 24-hour period.

Side effects

  • In children:
    • Antihistamines may make young children sleepy or may stimulate the nervous system, causing hyperactivity. Don't give antihistamines to your child unless you've checked with the doctor first.
    • In rare cases, diphenhydramine (especially forms of it that are applied to the skin) can cause severe side effects in children, such as hallucinations, tremors, and coma.
  • In older children and adults:
    • Antihistamines may cause drowsiness.
    • Weakness, blurred vision, dry nose, mouth, and throat, difficulty urinating, or stomach upset also can occur.

If you have side effects, stop taking the medicine and call your doctor.

See Drug Reference for a full list of side effects. (Drug Reference is not available in all systems.)

Last Updated: July 8, 2009

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