What Are the Most Common Acyclovir Side Effects?

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  • Written By: Autumn Rivers
  • Edited By: Angela B.
  • Last Modified Date: 15 March 2019
  • Copyright Protected:
    Conjecture Corporation
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Acyclovir is an antiviral medication that is often prescribed to help reduce the symptoms of herpes while also slowing down its progression through the body. Patients should note, though, that this drug will not cure the virus and it has some side effects. Many side effects are considered minor, including nausea, diarrhea and headaches. Some acyclovir side effects, however, are more serious and should be reported immediately to a doctor. These may include mental issues, such as confusion and aggression, and physical symptoms that include seizures and sudden bruising.

Like many medications, this drug features a few side effects that most patients can tolerate, though even minor issues should be mentioned to a doctor at the next appointment. One example is nausea, which is sometimes followed by vomiting and loss of appetite. Diarrhea and headaches also may occur and, in fact, some patients just feel generally ill while taking this medication. Some swelling in the feet and hands, as well as a lightheaded feeling, also are minor acyclovir side effects noticed by some patients.


Not all acyclovir side effects are strictly physical, and some patients experience a mental change. For instance, patients may feel agitated while taking this medication, and this may become obvious to other people when patients show aggression for no apparent reason. They also may feel confused, and some also have hallucinations while on this medication. Additionally, drowsiness and a loss of coordination may occur, which can add to the confused and agitated state of mind that some patients experience. While these acyclovir side effects are not necessarily life-threatening, they are usually bothersome enough that many doctors will switch their patient to a different medication when possible, which is why these symptoms should be reported.

Other serious acyclovir side effects that should be immediately reported to a doctor include unusual bleeding or bruising on the body — both symptoms that can indicate an internal bleeding issue. Patients who notice a sudden decrease in the frequency of urination, in addition to lower back pain, are urged to tell their doctor, because these are considered serious side effects of the drug. It also is possible to be allergic to acyclovir, which is usually indicated by a sudden rash or hives all over the body, itchy skin and swelling. Serious allergic reactions may result in swelling in the face, in particular, as well as difficulty breathing — a life-threatening condition that warrants immediate medical attention.



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Post 3

@turkay1-- I think hair loss and hair thinning is a common side effect of acyclovir when it's taken at high doses.

I've been taking 800mg/day for the past year and I have started experiencing hair thinning. I have asked on several forums about it and it seems to be an issue for people on high doses like me. I don't think it happens at lower doses and for short treatments. If you're taking a high dose and if you will be taking it for a long time, you might want to watch out for this.

Aside from this, acyclovir gave me some nausea and upset stomach for a while but then my body adapted to it. I haven't had those issues for a long time.

Post 2

@turkay1-- I have no idea. I personally didn't experience hair loss, but I only took it for a month.

I'm actually not sure how I tolerated this drug for a month because it gave me diarrhea every single day. It was actually the reason I had to quit acyclovir because I had started to lose some weight and I was worried about dehydration.

Post 1

I noticed that hair loss is mentioned as a potential side effect of acyclovir. Has anyone actually experienced hair loss from it or is it rare?

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