Headache is a recognised side effect of aciclovir and valaciclovir. It has been reported commonly in people taking aciclovir tablets . If you develop a headache while taking aciclovir, it does not necessarily mean that something is wrong, but it is worth paying attention to how you feel and whether the headache continues or becomes more severe.
For adults in the UK taking or considering aciclovir for cold sores, it can help to know what to expect and when to seek advice. Below, we explain how common headaches are with aciclovir, what may contribute to them, practical steps that may help, when to speak to a healthcare professional, and how aciclovir compares with valaciclovir.
Key things to know
- Headache is a commonly reported side effect of aciclovir tablets
- Headaches can range from mild to moderate and may settle as treatment continues
- No change required , particularly if you are losing fluids through vomiting or diarrhoea
- A severe headache with symptoms such as fever, neck stiffness or changes in vision needs prompt medical attention
How Common Is an Aciclovir Headache?
Headache is a recognised and commonly reported side effect of aciclovir tablets . It is listed among the more common side effects, along with effects such as nausea and dizziness.
This does not mean that everyone taking aciclovir will develop a headache. If you do notice one after starting treatment, however, it can be a recognised side effect of the medicine.
If the headache is severe, does not improve, or is accompanied by other concerning symptoms, speak to your doctor or pharmacist rather than assuming that aciclovir is the cause.
Why Aciclovir Can Cause Headaches
The exact reason aciclovir can cause headaches is not fully understood. Aciclovir is an antiviral medicine that works by interfering with viral DNA replication. It is also mainly removed from the body through the kidneys.
Staying well hydrated is important while taking aciclovir, particularly if you are unwell or losing fluids. Dehydration can contribute to headaches, so maintaining adequate fluid intake may help if dehydration is playing a role .
It is also important to remember that a headache while taking aciclovir may have another cause. Stress, illness, lack of sleep, dehydration and other medicines can all contribute to headaches. If you are unsure what is causing yours, a pharmacist or doctor can help you work through the possible causes.
Headache Alongside Other Common and Serious Side Effects
You may experience a headache alongside other recognised side effects of aciclovir, such as:
- Nausea
- Dizziness or lightheadedness
- Digestive symptoms, such as diarrhoea or vomiting
- Fatigue
Having a headache together with one of these effects does not automatically mean that there is a serious problem. However, if your symptoms are severe, persistent or getting worse, speak to a healthcare professional for advice.
If you develop unusual neurological symptoms, confusion, severe drowsiness, seizures or other significant changes in your condition, seek medical attention promptly. These symptoms should not simply be assumed to be a routine side effect.
What Does an Aciclovir Headache Typically Feel Like?
There is no single type of headache that everyone experiences with aciclovir. A medicine-related headache may feel like a general ache or pressure , but the exact symptoms can vary from person to person.
A headache can also have a completely different cause, particularly when you are already unwell with a viral infection. For example, poor sleep, dehydration, stress or the infection itself may contribute to how you feel.
If your headache is severe, sudden, unusual for you, or occurs alongside symptoms such as changes in vision, weakness, confusion, fever or neck stiffness, seek medical advice promptly rather than assuming it is simply a side effect of aciclovir .
Does Valaciclovir (Valtrex) Cause Headaches Too?
Yes. Headache is also a recognised side effect of valaciclovir. Valaciclovir is converted into aciclovir in the body, so the two medicines have similar active ingredients and can have some similar side effects.
If you develop headaches while taking aciclovir and are considering switching to valaciclovir, changing treatment may not necessarily prevent headaches from occurring . However, people can respond differently to medicines, so speak to your prescriber or pharmacist before making any change to your treatment.
Valaciclovir and aciclovir can also have different dosing schedules depending on what they are being used to treat. If taking medicine several times a day is difficult for you, mention this to your prescriber. They can explain whether an alternative treatment or dosing schedule is appropriate.
Managing an Aciclovir Headache
If you develop a mild headache while taking aciclovir, a few simple measures may help:
- Drink enough fluids to stay hydrated, particularly if you have been vomiting, have diarrhoea or are otherwise losing fluids
- Take your medicine as directed. Aciclovir tablets can be taken with or without food. If you find that taking your medicine with food feels more comfortable, you can discuss this with your pharmacist
- Paracetamol may be suitable for some people, but it is sensible to check with a pharmacist or healthcare professional before taking additional medicines , particularly if you have other medical conditions or take other medicines
- Rest somewhere quiet and comfortable if a headache develops
These steps cannot guarantee that your headache will improve, and you should not change or stop your antiviral treatment without advice. If your headache is severe, persistent or getting worse, speak to your doctor or pharmacist.
If you have kidney problems, it is particularly important to follow the prescribed aciclovir dose and stay appropriately hydrated. Your prescriber may need to consider your kidney function when deciding which dose is suitable for you.
A Note on Other medicines and Kidney Problems
Headaches can have many possible causes, including other medicines you may be taking. For example, some medicines, including sildenafil and tadalafil, can also cause headaches .
If you take other medicines and develop headaches while using aciclovir, tell your pharmacist or prescriber. They can consider your medicines together and help determine whether the headache could be related to aciclovir, another medicine, dehydration, your underlying illness or another cause.
Kidney function is also important when taking aciclovir because the medicine is mainly cleared through the kidneys. If you have kidney disease or have been told that your kidney function is reduced, make sure your prescriber knows before treatment is started.
When to Seek Medical Advice
Most headaches while taking aciclovir are not serious, but some symptoms need medical attention. Contact a No change required. This is standard UK usage promptly if you have:
- Severe or sudden headache, especially if it is the worst headache you have experienced
- A headache with fever and a stiff neck
- Changes in your vision alongside the headache
- A headache that keeps getting worse rather than improving after a few days
- A headache with confusion, unusual drowsiness or difficulty staying awake
- A headache alongside reduced urine output or swelling, as these can be signs of kidney problems and may require medical assessment
These symptoms can have causes other than aciclovir, but they should not automatically be treated as a routine medicine side effect. If you are concerned, speak to a doctor, pharmacist or another appropriate healthcare professional.
If Headaches Persist
If your headaches continue or become difficult to manage, speak to your prescriber or pharmacist rather than stopping treatment without advice. They can review your symptoms, other medicines you take and whether aciclovir is still the most suitable option.
For cold sores on the lips and face, topical aciclovir cream may be another treatment option. Because it is applied directly to the affected area, less of the medicine is absorbed into the body compared with oral treatment . Whether it is suitable depends on the location and severity of the cold sore and your individual circumstances.
If you have been prescribed oral aciclovir, try to follow the prescribed course unless a healthcare professional advises you to stop. If the headache is mild and manageable, you can ask a pharmacist about ways to manage it while completing your treatment. If the headache is persistent, severe or worrying you, contact your prescriber so they can decide whether you need a different approach.
Considering treatment for cold sores, or concerned about a side effect from your current treatment? Start a free online consultation with a UK prescriber .
Available Cold Sore Treatments
| Treatment | Price from |
|---|---|
| Aciclovir tablets | £12.99 |
| Aciclovir 5% cream | £8.99 |
| Valaciclovir | £18.99 |
| Valtrex | £34.99 |
Prices update live and may change.
Medical Disclaimer
This page provides general information about headaches and other possible side effects associated with aciclovir and valaciclovir. It is intended for information only and is not a substitute for personalised medical advice, diagnosis or treatment.
If you experience a severe or sudden headache, a headache with fever and neck stiffness, changes in vision, confusion, or any other worrying symptoms, seek medical attention promptly .
If you have concerns about your treatment or experience side effects, speak to your doctor, pharmacist or another qualified healthcare professional. If you think you may be having a serious side effect or an allergic reaction, seek appropriate medical advice without delay.
