What are the side effects of aciclovir?

Aciclovir is a drug you might be prescribed to take for certain types of viral infections. It’s used for cold sores around the mouth, shingles, chickenpox, and genital herpes.

Like with any medication, it’s possible to experience unwanted side effects from aciclovir tablets. In this guide we will outline theways aciclovir can be taken, including as an injection, as an eye drop, or as a cream. These forms may have slightly different side effects – and you should always check the leaflet in your medication packet for more information.

Common aciclovir side effects

Between 1 person in 10 and 1 person in 100 will experience one or more of these side effects:

• nausea (feeling sick)
• vomiting
• diarrhea
• headaches
• feeling more sensitive to sunlight

Uncommon aciclovir side effects

Between 1 person in 100 and 1 person in 1,000 will experience the following side effects:

• tiredness - feeling fatigued throughout the day
• constipation - having trouble going to the toilet
• mood changes – this might be agitation, hallucinations, confusion dizziness, or drowsiness
• sign(s) of kidney problems – this can include changes in the amount of urine and/or abnormal back or side pain
• vertigo – feeling like you or your surroundings are spinning and whirling, which can make you feel dizzy and affect your balance
• painful joints or muscles – muscles aching
• oedema – this is when extra water builds up in parts of your body, which could lead to swelling and other issues
• itching or rashes – these might be red patches on your skin

Rare aciclovir tablet side effects

Between 1 person in 1,000 and 1 person in 10,000 will experience the following rare side effects:

• hepatitis – this is a condition caused when there’s inflammation of the liver
• seizures – there are different typesof types of seizures, but they might be recognised if you’ve got symptoms like temporary confusion, uncontrollable jerking of arms or legs, or loss of consciousness
• decreased white cells in your body – this means your immunity is lower and you’re more likely to fall ill with infections
• Stevens–Johnson syndrome – this is a rare disorder that needs immediate treatment, which affects the skin and mucous membranes, and which is recognised via symptoms and then a painful red or purple aciclovir rash that spreads and blisters
• allergic reaction – this could mean you have trouble breathing, tongue or throat swelling, rash, or hives, and this needs immediate treatment, since it could be fatal
• coma – prolonged loss of consciousness

What is the most common side effect of aciclovir?

The most common side effects of aciclovir tablets are nausea and vomiting, when taken for shorter time periods (less than six months). For people taking aciclovir for longer than six months, the most common side effects include headache, diarrhoea, nausea, and vomiting.

Does aciclovir make you tired?

Aciclovir can make you feel tired, and fatigue is reported as a mild side effect by some people. But, it’s also important to be aware that a more serious side effect of aciclovir is low red blood cells, which can be very dangerous. Low red blood cell levels can also cause tiredness. Talk to your doctor if you experience tiredness when taking aciclovir.

Can aciclovir cause thrush?

No, there is no reason to believe aciclovir will cause thrush. Thrush is a yeast infection caused by a fungus called Candida. Aciclovir is an antiviral drug that is used to treat viruses that cause herpes, shingles, and chickenpox. It is true that some antibiotics can cause thrush. This is because they kill the bacteria in your body that normally fight off Candida.

However, antivirals don’t kill bacteria in your body, as antibiotics do. They only target viruses, which are a different type of organism to bacteria.

Before you start taking aciclovir, it’s important to let your doctor know if you’re taking any other medication, including any over-the-counter medications, supplements, and herbal remedies. This is because different treatments can interact with each other and cause some negative issues.

Some other medications that can interact with aciclovir include those used for:

• HIV/AIDS – zidovudine
• bacterial or fungal infections – amphotericin B, foscarnet, gentamicin, and kanamycin
• cancer – talimogene laherparepvec, and cisplatin
• pain relief – Motrin and ibuprofen
• stomach ulcers – cimetidine
• gout – probenecid
• asthma – aminophylline or theophylline

You may be more likely to experience aciclovir tablet side effects if:

You have kidney problems

Your body might not be able to clear the drug from your system as well. Because of this, the level of the drug increases in your body, potentially causing issues. It’s also possible that aciclovir decreases your kidney function, so you’ll also need to speak to your doctor about whether your dose needs changing.

You are pregnant

There is no evidence to suggest that aciclovir is a risk to a fetus, but you should still talk to your doctor if you’re pregnant or are planning to conceive. You’ll need to carefully consider the benefits and potential risks before deciding to take aciclovir.

You are breastfeeding Aciclovir may affect a child being breastfed, since it can pass into breast milk. If you are breastfeeding, you should tell your doctor and get some advice about whether you can take this medication whilst breastfeeding.

You have an allergy to aciclovir

Aciclovir should not be used by people who are allergic to the drug itself or any of its ingredients.

Aciclovir side effects could happen to anyone (although they don’t happen to everyone). The best way to lower your risk of side effects is to talk with your doctor and tell them any relevant past or recent medical information and they will be able to assess whether aciclovir is suitable for you.

“Most people don’t experience any aciclovir side effects. And among those that do, they are usually fairly mild. While there are certainly some unpleasant side effects, it’s important to weigh this up against how you’d feel if you didn’t take the medication."

— Dr Brenda Ikeji, Medical Editor

To start with, it’s always a good idea to take a look at the patient information leaflet, which comes with your medication. You can use this to become familiar with the side effects, what they might look like and how common each one might be. Not everyone experiences side effects, but being informed is important.

We would also recommend that you keep a notebook of all your appointments with your doctor and any tests you might end up doing to check your response to aciclovir. In this notebook, you should write down what times you’re taking aciclovir, what time you experience side effects (if any) and when they get better or worse. Trends like worsening of side effects after you take aciclovir should be reported to your doctor.

Your doctor will also want to rule out other causes, because many drugs can cause some similar symptoms to aciclovir, such as weakness and fatigue. Your doctor will check if you’re taking any other medicine before they prescribe aciclovir.

If you are experiencing unwanted side effects of aciclovir tablets, check with a doctor before stopping treatment. Unless you’re having a severe reaction, such as an allergic reaction, it’s usually best to keep taking your antivirals.

That said, even if you’re only experiencing mild symptoms, you should let your doctor know immediately. They’ll let you know whether you should continue until you finish the prescription or if you should stop. Don’t just stop taking the medication yourself, since it might mean that your infection may not be completely treated or may become more difficult to treat.

You should also look out for signs of an emergency. The symptoms might include agitation, extreme sleepiness, loss of consciousness, seizures, or difficulty breathing. Call 999 if you have any of these reactions.

Yes, for most people, taking aciclovir is worth the risk of experiencing side effects. Most people don’t experience side effects, and among those who do, they tend to be fairly mild.

It is also a drug that people usually only use for a short period of time, rarely more than 5 to 10 days at most, which makes serious long-term side effects less likely.

If you're worried about the side effects of aciclovir tablets, it's best to do some research. You should first read the patient information leaflet that comes with your medication. You could also talk to your doctor to see if they have any additional resources you could read to better inform you and put your mind at ease.

A doctor will only give you aciclovir if the benefits outweigh the risks. On the whole, you should remember that your doctor has prescribed this medication because they’ve judged that the benefit to you is greater than the risk of side effects. However, if you’re worried about taking the medication, make sure you discuss your concerns with your doctor.