Side Effects Of Diphenhydramine

Like all medicines, diphenhydramine can cause side effects, although not everyone gets them. However, you may be more likely to get them if you're over 65.

Common side effects of diphenhydramine

These common side effects of diphenhydramine happen in more than 1 in 100 people. There are things you can do to help cope with them:

Speak to a doctor or pharmacist if the advice on how to cope does not help and a side effect is still bothering you or does not go away.

Serious side effects

Call a doctor or call 111 straight away if:

• you have a fast or irregular heartbeat (palpitations)
• you feel any numbness or pins and needles
• you feel very restless
• you're feeling confused - you're unable to concentrate or think clearly, or have muddled thoughts

Call 999 if:

Do not drive yourself to A&E.

The person you speak to at 999 will give you advice about what to do.

Serious allergic reaction

In rare cases, it's possible to have a serious allergic reaction (anaphylaxis) to diphenhydramine.

Call 999 now if:

• your lips, mouth, throat or tongue suddenly become swollen
• you're breathing very fast or struggling to breathe (you may become very wheezy or feel like you're choking or gasping for air)
• your throat feels tight or you're struggling to swallow
• your skin, tongue or lips turn blue, grey or pale (if you have black or brown skin, this may be easier to see on the palms of your hands or soles of your feet)
• you suddenly become very confused, drowsy or dizzy
• someone faints and cannot be woken up
• a child is limp, floppy or not responding like they normally do (their head may fall to the side, backwards or forwards, or they may find it difficult to lift their head or focus on your face)

You or the person who's unwell may also have a rash that's swollen, raised, itchy, blistered or peeling.

These can be signs of a serious allergic reaction and may need immediate treatment in hospital.

Long-term side effects

It's possible to become dependent on diphenhydramine if you take it for too long without a break.

Follow the instructions that come with the medicine and only take diphenhydramine for a very short time, unless your doctor gives you different advice.

Other side effects

These are not all the side effects of diphenhydramine. For a full list, see the leaflet inside your medicine packet.

Reporting side effects

You can report any suspected side effect using the Yellow Card safety scheme.

Visit the Yellow Card website for more information about reporting side effects.

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