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Histergan Tablets

Active Ingredient:
diphenhydramine hydrochloride
Norma Chemicals Limited See contact details
ATC code: 
About Medicine
The Patient Information Leaflet (PIL) is the leaflet included in the pack with a medicine.
Last updated on emc: 03 May 2024

Below is a text only representation of the Patient Information Leaflet (ePIL).

The text only version may be available in large print, Braille or audio CD. For further information call emc accessibility on {phone} 0800 198 5000. The product code(s) for this leaflet is: PL 00386/5008.

Histergan Tablets

Patient Information Leaflet

Histergan Tablets

Diphenhydramine Hydrochloride

Read all of this leaflet carefully before you start using this medicine because it contains important information for you.

Always use this medicine exactly as described in this leaflet or as your doctor or pharmacist has told you.

  • Keep this leaflet. You may need to read it again.
  • Ask your pharmacist if you need more information or advice.
  • If you get any side effects, talk to your doctor or pharmacist. This includes any possible side effects not listed in this leaflet. See section 4.
  • You must talk to a doctor or pharmacist if your symptoms worsen or do not improve.

This leaflet contains the following information.

1. What Histergan Tablets are and what are they used for?
2. What you need to know before you use Histergan Tablets
3. How to use Histergan Tablets
4. Possible side effects
5. How to store Histergan Tablets
6. Contents of the pack and other information

1. What Histergan Tablets are and what are they used for?

Histergan Tablets contain the following active ingredient: Diphenhydramine hydrochloride. Diphenhydramine hydrochloride is an antihistamine which works by blocking the body’s response to histamine, which is an agent responsible for causing allergic responses such as hay fever, stings and rashes. Histamine is also involved in the brain’s waking system so diphenhydramine hydrochloride can help alleviate temporary sleeplessness.

2. What you need to know before you use Histergan Tablets
Do not use Histergan Tablets:
  • if you are allergic to diphenhydramine hydrochloride or any of the ingredients listed in section 6 of this leaflet
  • if you have a peptic ulcer
  • if you have a blockage between your stomach and small intestine.

Warnings and precautions

Talk to your doctor or pharmacist before taking Histergan Tablets:

  • if you suffer from myasthenia gravis (abnormal muscle function)
  • if you suffer from seizures or have epilepsy
  • If you asthma, bronchitis or Chronic Obstructive Pulmonary Disease (COPD)
  • if you have narrow-angle glaucoma
  • if you have an enlarged prostate
  • if you have difficulty urinating
  • if you have moderate to severe liver or kidney problems
  • if you are elderly, particularly if you also suffer from confusion.

This medicine is for short term use. It may not work as well if you use it continuously. If your symptoms persist, see your doctor for advice.

Other medicines and Histergan Tablets:

Tell your doctor or pharmacist if you are taking, have recently taken or might take any other medicines, including:

  • Other antihistamines including those used on your skin and in cough and cold medicines
  • Tranquillisers or anxiolytics (sedatives) used to treat anxiety e.g. diazepam
  • Hypnotics (e.g. nitrazepam) used to help you sleep better
  • Monoamine oxidase inhibitors (MAOIs) for depression (e.g. phenelzine) or if you have stopped taking an MOAI within the last two weeks
  • Metoprolol (a beta blocker) used to treat high blood pressure, angina, irregular heart beat or overactive thyroid
  • Venlafaxine used to treat depression
  • Anticholinergics which relax smooth muscles and are used for example in Parkinson’s disease, irritable bowel syndrome and incontinence e.g. procyclidine, trihexyphenidyl, atropine, oxybutynin, fesoterodine
  • Tricyclic antidepressants (e.g. imipramine, amitriptyline).

Histergan Tablets with alcohol:

While taking Histergan Tablets avoid alcoholic drink.

Pregnancy and breast-feeding:

Do not take Histergan Tablets if you are pregnant or breast-feeding.

Driving and using machines:

This medicine causes drowsiness and sedation and may also cause dizziness, blurred vision, disturbance in attention and slower reaction times. Do not drive or operate machinery while you are affected in this way.

Histergan Tablets contain lactose and sucrose:

If you have been told by your doctor that you have an intolerance to some sugars, contact your doctor before taking this medicinal product.

3. How to use Histergan Tablets

Always use this medicine exactly as described in this leaflet or as your doctor or pharmacist has told you. Check with your doctor or pharmacist if you are not sure. The recommended dose is:

For the treatment of hay fever, stings, rashes and other minor allergies:

Adults and children over 12 years: 1 or 2 tablets three or four times a day or as prescribed by a doctor.

Not recommended for children under 12 years of age.

For use as a temporary sleep aid:

Adults: 1 or 2 tablets to be taken at bedtime or after retiring when sleep is not readily achieved.

Do not take a repeat dose in the same night.

Not recommended as a sleep aid in children under 16 years of age.

If you take more Histergan Tablets than you should:

Seek medical attention as soon as possible. When seeking medical advice you should, if possible, take the medicine and this leaflet with you provided it doesn’t cause a delay.

If you have any further questions on the use of this medicine, ask your doctor or pharmacist

4. Possible side effects

Like all medicines, this medicine can cause side effects, although not everybody gets them.

If any of the following occur STOP TAKING the tablets IMMEDIATELY and contact your doctor, as these may be signs of an allergic reaction:

  • Difficulty breathing or shortness of breath, swelling of the face, mouth or throat
  • Rash, hive (itchy, raised red weals).

If you notice any of the following effects tell your doctor straightaway:

  • Faster heartbeat, irregular heartbeat
  • Fits, difficulty making or controlling movements.

Tell your doctor, pharmacist or nurse if you suffer from any of the following other effects:

Common effects (may affect up to 1 in 10 people):

  • Sedation, drowsiness, dizziness, unsteadiness, disturbance, inattention
  • Dry mouth
  • Fatigue.

Other effects (frequency not known – cannot be estimated from the data available):

  • Palpitations (feeling your heartbeat)
  • Headache, tingling or numbness (pins and needles)
  • Depression, sleep disturbances
  • Confusion, excitation e.g. increased energy, restlessness, nervousness (the elderly are more likely to experience these effects)
  • Difficulty urinating or inability to pass urine
  • Thicker bronchial mucus
  • Blurred vision
  • Feeling or being sick, stomach problems
  • Muscle twitching.

Reporting of side effects

If you get any side effects, talk to your doctor or pharmacist or nurse. This includes any possible side effects not listed in this leaflet. You can also report side effects directly via the Yellow Card Scheme at or search for MHRA Yellow Card in the Google Play or Apple App store. By reporting side effects you can help provide more information on the safety of this medicine.

5. How to store Histergan Tablets

Keep this medicine out of the sight and reach of children. Store below 25°C. Do not use this medicine after the expiry date which is stated on the carton and blister pack. The expiry date refers to the last day of that month.

Do not throw away any medicines via wastewater or household waste. Ask your pharmacist how to throw away medicines you no longer use. These measures will help protect the environment.

6. Contents of the pack and other information

What Histergan Tablets contain:

The active substance is diphenhydramine hydrochloride, 25mg. The other ingredients are: lactose, corn starch, povidone, magnesium stearate, Opaseal (polyvinyl acetate phthalate, ethyl acetate and stearic acid), sucrose, calcium carbonate, talc, acacia, titanium dioxide E171, Opalux Pink AS 1537 (E127 erythrosine), Opaglos 6000 (carnauba wax, beeswax), silicone fluid.

What Histergan Tablets look like and the contents of the pack:

Histergan Tablets are pink, sugar coated, tablets and are supplied in packs of 8, 16 or 20 tablets. Not all pack sizes may be marketed.

Marketing Authorisation Holder and Manufacturer:

The marketing authorisation holder is:

Norma Chemicals Ltd.
51-53 Stert Street
OX14 3JF

The EEA site of batch release is:

Surepharm Services Ltd.
Bretby Business Park
Burton upon Trent
DE15 0YZ


Wasdell Packaging Ltd.
Euroway Industrial Estate

This Leaflet was last revised in September 2017



Norma Chemicals Limited
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51-53 Stert Street, Abingdon, Oxon, OX14 3JF
Medical Information Direct Line
+44 (0)1235 538 700
Medical Information e-mail
[email protected]
Customer Care direct line
+44 (0)1235 538 700
Medical Information Fax
+44 (0)1235 538 800
Adverse event reporting email
+44 (0)1235 538 700