Antihistamines are medications that are used to manage symptoms of allergic reactions. There are different types available, and you can often purchase them over the counter.  

  1. Treat allergic reactions.
  2. Available in capsules, tablets, syrups, creams, liquids, gels, nasal sprays and eye drops.
  3. Older types of antihistamines can have a tranquilising effect.

If you have any concerns relating to allergies, you can speak with one of GMC-registered clinicians via our online video consultation service. Our clinicians are available from 9.30am to 4.30pm, five days a week.

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What are antihistamines?

Anaphylaxis is a medical emergency and can be extremely serious if it is not treated promptly. If someone is experiencing symptoms of anaphylaxis (feeling lightheaded or faint, difficulties breathing, wheezing, a rapid heartbeat, clammy skin, confusion and anxiety and has collapsed or lost consciousness) or other additional allergy symptoms (hives, sickness, swelling or abdominal pain) you should call 999 immediately. 

Antihistamines are medications that are prescribed or purchased to treat symptoms related to allergic reactions. These symptoms are typically associated with insect bites and stings, hay fever and hives. Due to their sedative effects, older types may also be prescribed to treat insomnia in the short term.

What can insect bites and stings cause?

Insect bites and stings rarely cause anything more severe than irritation, which usually resolves within a few days. The most common bites and stings are those associated with fleas, wasps, hornets, bees, mosquitoes, ticks, horseflies, midges and spiders. Occasionally, they can lead to more serious allergic reactions, called anaphylaxis, which requires immediate medical attention. Tick bites may also cause Lyme disease, although only in a small number of cases. 

What are the symptoms of insect bites and stings?

Symptoms of insect bites and stings include red lumps that can be itchy or painful to touch. Swelling may also occur that is hot to the touch. Should you have difficulty breathing or experience dizziness, this could be anaphylaxis. 

Treatment for bites and stings can be undertaken at home in most cases. If the sting is still present, remove it and wash the area involved. A cold compress can help to manage irritation, while raising the part of the body afflicted (when possible) can reduce swelling. You should avoid irritating the area further, and taking antihistamines can also help with the irritation. 

If your symptoms do not improve over the course of a few days, you have been stung or bitten around / in the mouth and eyes, the swelling is larger than 10cms around the bite, you have developed an infection or if flu-like symptoms are present, you should seek medical help.

What is hay fever?

Hay fever is an allergic reaction to pollen, the levels of which are higher in the spring and summer months between March and September. Symptoms include coughing, sneezing, runny nose, itchy eyes, mouth and throat, watery eyes, a reduced sense of smell, headaches in the temple or forehead, earache and fatigue. If you also suffer from asthma, it may also lead to difficulties breathing, tightness in the chest and wheezing. 

What symptoms does hay fever cause?

The symptoms of hay fever are similar to those of the common cold, but while the common cold clears up over the course of a week or so, hay fever can last for months. There is no cure for hay fever and you can’t avoid its symptoms, but you can manage the severity of them. Putting a small amount of Vaseline under the nostrils (which traps the pollen), wearing wraparound sunglasses (which prevents pollen from affecting the eyes), washing your clothes regularly, keeping windows and doors shut where possible, vacuuming and dusting regularly and using HEPA filters on your air conditioning and vacuum cleaner are measures that can all help. 

Antihistamines are the most common treatment for hay fever. More severe cases may also be treated by an immunologist, who can slowly introduce pollen into your system over the winter months to build up an immunity to your allergy.

What is hives?

Hives can appear as red patches or small spots anywhere on the body, and occur at any age. The rash is typically itchy, and causes a burning or stinging sensation. Hives presents when a high level of histamine, and other naturally occurring chemicals in the body, is released in response to what your immune system perceives as an invading substance. These can relate to stings and bites, food, pollen or other plant substances, latex, dust, chemicals, heat, sunlight, water, medications, infections or stress

How is hives treated?

The main treatment for hives, other than avoiding triggers where possible, is over the counter antihistamines, advice for which you can get from your local pharmacy. You should speak to your doctor if your symptoms have not improved after a few days, if it is spreading, or you have a fever. It is essential that you seek immediate medical attention if you are having difficulty breathing or swallowing, you are vomiting or fainting, you experience dizziness, have an increased heart rate or notice swelling of the mouth, throat or face.

If you would like to discuss allergies and treatment with antihistamines with a doctor, our GPhC-registered clinicians are available for consultations via our online video service.You can make an appointment to speak with them between 9.30am and 4.30pm, Monday to Friday. They can also issue referrals to specialists for treatment and fit notes, where suitable.  

Page last reviewed:  23/06/2020
Side effects and warnings

What side effects can antihistamines have?

Side effects of antihistamines may vary, depending on the treatment. It’s therefore important that you carefully read the patient information leaflet that comes with the medication, or discuss any potential side effects with your prescribing doctor or pharmacist. 

One of the most commonly used antihistamines contains the active ingredient cetirizine hydrochloride, the side effects of which include: 

Common (affects up to one in ten patients): sleepiness, dizziness, headaches, diarrhoea, nausea, dry mouth, fatigue, pharyngitis and cold-like symptoms of the nose in children.

Uncommon (affects up to one in 100 patients): anxiety, strange sensations of the skin, stomach ache, irritated skin, rashes, fatigue and generally feeling unwell. 

Rare (affects up to one in 1,000 patients): depression, hallucinations, aggression, confusion, sleeplessness, rapid heartbeat, abnormal liver function test results, hives, oedema and weight gain. 

Very rare (affects up to one in 10,000 patients): unusual bleeding, bruising, twitches, involuntary movements, contractions of the muscles, tremors, unusual tastes, altered vision, problems focusing, uncontrolled eye movements, fixed drug eruption and abnormal urination.

The following side effects have been reported, but there is not enough data to indicate their frequency: increased appetite, memory loss and forgetfulness, vertigo, urinary retention, itching, joint pain and a rash with blisters that contain pus.

Warnings and precautions when using antihistamines

The following information is related to the antihistamine cetirizine hydrochloride, and may therefore not be relevant to your medication. You should speak to your prescribing doctor or pharmacist for further information about your treatment.

If you experience the following symptoms when taking cetirizine hydrochloride, you should discontinue use and seek immediate medical attention: swelling of the face or throat, convulsions or suicidal thoughts. You should also avoid the use of this medication if you have severe kidney disease.

If you have a medical condition, it’s important that you inform your prescribing doctor before starting treatment. Antihistamines may not be suitable to use if you have any of the following conditions: kidney problems, problems passing urine and epilepsy. 

Taking antihistamines can affect the results of allergy tests, and you should avoid using them at least a week in advance of the tests.

If you are currently taking other medication, you should inform your prescribing doctor (where relevant) before starting treatment. Further information is also available on the patient leaflet, which is provided with your medication.

What types of antihistamines are available?

There are broadly two types of antihistamines: the older types and the newer forms. The older ones produce a sedative effect that may be unsuitable for many people; these include chlorphenamine, hydroxyzine and promethazine. Newer types include cetirizine, loratadine and fexofenadine. Some types of antihistamine may be more suitable for you than other types, and you should discuss their suitability with your prescribing doctor if you are unsure. 

Page last reviewed:  23/06/2020
Questions and Answers

Are antihistamines safe to use during pregnancy or breastfeeding?

Many antihistamines are not recommended for use when pregnant or breastfeeding, so it is important that you speak with your doctor or pharmacist before starting treatment.

Can antihistamines affect my ability to drive?

This will likely depend on which type of antihistamine you are taking. Newer versions should have little to no effect on your ability to drive, but older types will likely cause drowsiness, meaning you should avoid operating heavy machinery during treatment. 

Is it safe to consume alcohol whilst taking antihistamines?

It depends on the specific treatment. Cetirizine, for example, is not affected by alcohol consumption, while older versions can increase the sedative effect of alcohol. If you are unsure, you should consult with your prescribing doctor or pharmacist.

Can I buy antihistamines over the counter?

Some antihistamines are only available with a prescription, but many are available for purchase at your local pharmacy or supermarket.

How can I buy antihistamines online?

Our GPhC-registered clinicians can discuss antihistamines with you via our online video consultation service. They are available from 9.30am-4.30pm, Monday to Friday. They can also provide fit notes and referral to specialists for treatment, where appropriate. 

Page last reviewed:  23/06/2020

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