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You are here : 3-RX.com > Drugs & Medications > Detailed Drug Information (USP DI) > Antihistamines : Side Effects

Antihistamines (Systemic)

Antihistamines | Before Using | Proper Use | Precautions | Side Effects | Additional Information

Side Effects of This Medicine

Along with its needed effects, a medicine may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

    Check with your doctor immediately if the following side effect occurs:

      Less common or rare


      Less frequent or rare with azatadine, cetirizine, clemastine, cyproheptadine, desloratadine, dexchlorpheniramine, diphenhydramine, or loratadine

        Fast or irregular heartbeat; fever; abdominal or stomach pain; burning; chills; clay-colored stools or dark urine; cough; diarrhea; difficulty swallowing; dizziness; fast heartbeat; fever; headache; hives; itching; prickly sensations; puffiness or swelling of the eyelids or around the eyes, face, lips or tongue; redness of skin; seizures; shortness of breath; skin rash; swelling; tightness in chest; tingling; unusual tiredness or weakness; wheezing

    Also, check with your doctor as soon as possible if any of the following side effects occur:

      Less common or rare

        Sore throat; unusual bleeding or bruising; unusual tiredness or weakness

      Symptoms of overdose

        Clumsiness or unsteadiness; convulsions (seizures); drowsiness (severe); dryness of mouth, nose, or throat (severe); feeling faint; flushing or redness of face; hallucinations (seeing, hearing, or feeling things that are not there); shortness of breath or troubled breathing; trouble in sleeping

Other side effects may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. However, check with your health care professional if any of the following side effects continue or are bothersome:

    More common

      Drowsiness; dry mouth, nose, or throat; gastrointestinal upset, stomach pain, or nausea; headache; increased appetite and weight gain; thickening of mucus

    Less common or rare

      Acid or sour stomach; belching; blurred vision or any change in vision; clumsiness or unsteadiness; body aches or pain; confusion (not with diphenhydramine); congestion; constipation; cough; diarrhea; difficult or painful urination; difficulty in moving; difficult or painful menstruation; dizziness (not with brompheniramine or hydroxyzine; drowsiness (with high doses of desloratadine and loratadine); dryness of mouth, nose, or throat; early menstruation; fast heartbeat; fatigue; fever; gastrointestinal upset, stomach pain or nausea; heartburn; hoarseness; increased appetite and weight gain; increased sensitivity of skin to sun; increased sweating; indigestion; loss of appetite; joint pain; muscle aching or cramping; muscle pains or stiffness; nausea; nightmares (not with azatadine, chlorpheniramine, cyproheptadine, desloratadine, hydroxyzine, or loratadine); ringing or buzzing in ears; runny nose; skin rash; swollen joints; stomach discomfort, upset or pain; tender swollen glands in neck; thickening of mucus; tremor; unusual excitement, nervousness, restlessness, or irritability; vomiting

Other side effects not listed above may also occur in some patients. If you notice any other effects, check with your health care professional.

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Antihistamines: Precautions


Antihistamines: Additional Information

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