Antihistamines
- Madeeha Waheed, Oncology Pharmacist at Bupa, Medical Policy Team
Antihistamines are medicines that you take to stop the symptoms of an allergic reaction like hay fever. You may also take them for things like insect bites and stings, or travel sickness.
Uses of antihistamines
Antihistamines help to ease allergy symptoms, such as sneezing, a runny nose, a skin rash or itching. You can buy some antihistamines over the counter from a pharmacy. Some are only available on prescription.
Antihistamines may be helpful for allergic conditions such as:
- hives (urticaria)
- drug allergies
- itchy eczema or dermatitis
- allergic conjunctivitis (sore, itchy eyes)
- allergic asthma
Antihistamines may also help to ease:
- feeling sick (nausea) and vomiting, including travel sickness
- vertigo (feeling like everything around you is spinning)
- insect bites and stings
Not everyone can take antihistamines and the best allergy medicine for you will depend on your circumstances. Talk to a pharmacist or GP before you take these medicines for the first time. And read the patient information leaflet that comes with your medicine.
If you’re pregnant or breastfeeding, speak to your GP or pharmacist before you take an antihistamine. They can say whether it’s safe to take. Some antihistamines can affect your baby.
Anaphylaxis
If someone has anaphylaxis or suspected anaphylaxis, get urgent medical help. Anaphylaxis is a serious allergic reaction that can quickly escalate and needs treatment with an adrenaline injection. Antihistamines can be used once a patient is stabilised, for example to treat any skin symptoms after anaphylaxis..
Anaphylaxis can cause:
- difficulty breathing
- difficulty swallowing
- a swollen throat and tongue
- a fast heartbeat and pulse
- feeling faint and dizzy
- you to be sick
Anaphylaxis can be life-threatening. So, get medical help straightaway if you have these symptoms.
How antihistamines work?
Antihistamines work by blocking the effects of a chemical called histamine. Histamine is made and released by your immune system to help protect you from infections. It makes small blood vessels more ‘leaky’ around an area of damaged tissue. This lets immune cells and fluid go into the damaged area to fight infection and heal the tissues.
If you have an allergy, your immune system reacts to something that isn’t harmful like pollen. Your body then releases too much histamine. This can cause inflammation in your lungs, throat, nose, sinuses, digestive system and skin.
Types of antihistamines
Antihistamines come in different forms including:
- tablets and capsules
- liquids and syrups
- eye drops
- skin creams
- nasal sprays
There are two main types of antihistamines:
- sedating antihistamines, which may make you feel sleepy
- non-sedating antihistamines, which don’t usually make you feel sleepy
Sedating antihistamines
These are the older or ‘first generation’ antihistamines. They can make you feel sleepy, because the medicines move easily from your blood to your brain. This can slow down your thinking and movement and affect your concentration. If you get these effects, do not drive, cycle or operate machinery.
Your doctor may suggest that you take a sedating antihistamine if itching from an allergy affects your sleep.
Some of these medicines may help with travel sickness and vertigo. Sedating antihistamines that are available from pharmacies for allergies include:
- chlorphenamine maleate (eg Piriton)
- hydroxyzine hydrochloride
- cyproheptadine hydrochloride (eg Periactin)
- promethazine hydrochloride (eg Phenergan)
You may also be able to buy these antihistamines in an unbranded (generic) pack from a pharmacy.
There are some sedating antihistamines for allergies that can only be prescribed by your GP. These include a medicine called alimemazine.
If you have travel sickness or vertigo (dizziness) you can buy the following sedating antihistamines from a pharmacy.
- Cinnarizine (eg Stugeron)
- Promethazine teoclate (eg Avomine)
- Cyclizine
- Diphenhydramine (eg Nytol)
Non-sedating antihistamines
These are the newer ‘second generation’ antihistamines. They’re less likely to make you feel sleepy. But this varies from person to person, so be aware that you might still be affected by drowsiness.
Non-sedating antihistamines that you can buy from a pharmacy include:
- acrivastine (eg Benadryl Allergy Relief)
- cetirizine hydrochloride (eg Piriteze Allergy)
- loratadine (eg Clarityn Allergy)
You can also buy these antihistamines in a generic (unbranded) pack from a pharmacy.
Your GP can also prescribe other non-sedating antihistamines, such as fexofenadine.
Taking antihistamines
You can use antihistamines in different ways, depending on what’s causing your symptoms. For hay fever, you may need to take antihistamines throughout the spring and/or summer. If the allergen can be removed, you may only need to take antihistamines for a short time.
If you’re allergic to something you're often exposed to, you may need treatment for longer. Some people take antihistamines every day, but usually under medical guidance. If you find you need to take antihistamines long term (over several weeks), talk to your GP about this.
How you take your medicine will also depend on the form of antihistamine. Taking an oral antihistamine will be different from using a nasal spray or eyedrops. For information on how to take your medicine, read the patient information leaflet that comes with it. For further advice, speak to a pharmacist.
It’s best not to drink alcohol while you take any type of antihistamine. Alcohol can increase the sedative side-effects of antihistamines, so you’re even more likely to feel sleepy.
Interactions of antihistamines
Antihistamines can react with other medicines. Different antihistamines have different interactions. If you’re already taking other medicines, check with a pharmacist or GP before you take an antihistamine. And read the patient information leaflet that comes with your medicine. This will tell you which medicines could cause a problem when taken together.
Side-effects of antihistamines
Like all medicines, antihistamines can cause some side-effects. But they’re generally thought to be safe medicines.
Sedating antihistamines may well make you feel sleepy – you may even still feel sleepy the following day. They may also affect your coordination, movement and concentration. Some types of sedating antihistamines may affect you more than others. Non-sedating antihistamines may still make you feel sleepy, but it’s less likely. If you feel sleepy while taking any antihistamines, don’t drive, cycle or operate machines.
If you use an antihistamine nose spray, you may find it leaves a bitter taste in your mouth. This may be because you’re not using it properly, so speak to a pharmacist.
Children and older people may be more likely to get side-effects with some antihistamines. The patient leaflet that comes with your medicine will tell you about possible side-effects. These may be different for different antihistamines. If you have any questions, ask a pharmacist for advice.
Medicines checklist
Bupa's medicines checklist (PDF, 0.8MB), helps you understand what to check for before taking a medicine.
Antihistamines are used to ease allergy symptoms from conditions, such as hay fever, hives (urticaria), eczema or skin rashes. Antihistamines may also help to ease travel sickness and insect bites and stings.
See our uses of antihistamines section for more information.
You shouldn’t take antihistamines if you plan to drink any alcohol that day or night. Alcohol can increase the sedative side-effects of antihistamines, so you’re even more likely to feel sleepy.
Not everyone can take antihistamines either; it will depend on your circumstances. If you have a condition that affects your heart beat, for example, you probably won’t be able to take them. And if you’re pregnant or breastfeeding, some antihistamines can affect your baby.
Ask a pharmacist or GP whether it’s suitable for you. And read the patient information leaflet that comes with your medicine
If you take antihistamines to ease symptoms of an allergy, you’ll need to keep taking them while you have contact with the allergen. So, if you have hay fever, you may need antihistamines every day during the spring and/or summer. Some people do have to take antihistamines every day. This is usually done under guidance from their doctor. Seek medical help if you find yourself needing an antihistamine long term (outside of hay fever season).
If you think you’ve taken too much of any antihistamine, get medical help straightaway. Take the medicine packet(s) with you, so the doctor can see exactly which type of antihistamine you’ve taken and how many. It’s best to take someone with you just in case you need some support.
You should only take more than one antihistamine at a time if your doctor recommends this.
Be aware that a range of medicines you can buy at a pharmacy may contain antihistamines. This includes medicines for allergies, travel sickness, and coughs and colds. So it’s possible to take more than one antihistamine without realising it. It’s important to ask your pharmacist for advice if you plan on taking more than one of these medicines.
How long antihistamines take to work depends on the type you’re taking and what you’re taking them for. Antihistamines come in different forms which will also affect how quickly they work. Antihistamine tablets typically start to work within 30 minutes. They may reach their maximum effect in about two hours. Antihistamine nasal sprays work faster (within minutes), but only affect your nose.
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- Rachael Mayfield-Blake, Freelance Health Editor
