Indications
- Allergy symptoms such as sneezing, runny nose, itchy and watery eyes, hives and itching.
- Cough, in cough syrups where it is often combined with Ammonium Chloride, Sodium Citrate and Menthol.
- Prevention of motion sickness.
- Short-term help with occasional difficulty sleeping in adults.
- In hospital, the injection may be added to other treatment for serious allergic reactions.
How It Works
Diphenhydramine is an antihistamine. It blocks histamine, the natural chemical that causes allergy symptoms. It also enters the brain, where it causes drowsiness and calms the cough reflex, and it has a drying effect on the nose and mouth.
Dosage and Administration
- Adults and children 12 years and over, allergy: usually 25 to 50 mg every 4 to 6 hours, not more than 300 mg in 24 hours.
- Sleep: 50 mg about 30 minutes before bedtime, for a few nights only. See a doctor if sleeping problems last more than 2 weeks.
- Cough syrups: take the dose on the product label or as the doctor advises, because strengths differ.
- Children: only the dose stated on the label for that age or as a doctor advises. Do not give to children under 2 years, and do not use it to make children sleep.
- Injection: given only by a doctor or nurse.
Interactions
- Alcohol, sleeping tablets, sedatives, strong painkillers such as Tramadol, and other antihistamines increase drowsiness.
- Medicines with drying effects, such as Amitriptyline, add to dry mouth, constipation and difficulty passing urine.
- Avoid with, or within 14 days of stopping, a monoamine oxidase inhibitor (MAOI, an older type of antidepressant).
- It can raise blood levels of some medicines, such as Metoprolol.
- Do not take two products containing antihistamines at the same time.
Contraindications
- Allergy to diphenhydramine or any ingredient of the product.
- Newborn and premature babies.
- Breastfeeding mothers, unless a doctor advises it.
Side Effects
Common: drowsiness that can last into the next day, dizziness, dry mouth, blurred vision, constipation and difficulty passing urine. Older people may become confused. Children may become excited or restless.
Get urgent medical help for swelling of the face, lips or throat, difficulty breathing, fits, a fast or irregular heartbeat, hallucinations, or being unable to pass urine.
Pregnancy and Lactation
Pregnancy: occasional use is generally considered acceptable when a doctor advises it; avoid regular use near the time of delivery. Breastfeeding: it passes into breast milk, may make the baby drowsy or irritable and may reduce milk supply, so it is best avoided.
Precautions and Warnings
Do not drive or operate machinery if you feel sleepy. Ask a doctor before use if you have glaucoma, an enlarged prostate or trouble passing urine, asthma, epilepsy, heart rhythm problems, or liver disease. Older people should not use it as a sleeping aid because of the risk of confusion and falls. Never take more than the recommended dose.
Overdose
Overdose can be dangerous, especially in children. Signs include extreme drowsiness or agitation, hallucinations, hot and dry skin, wide pupils, a fast or irregular heartbeat and fits. Seek emergency medical help straight away.
Therapeutic Class
First-generation (sedating) antihistamine, also used as a cough suppressant and sleep aid.
Storage
Store below 30°C in a dry place, away from light and out of the reach of children.
Prepared by the Oshud Alo team from standard drug references. For information only; always follow your doctor's advice.