Does acyclovir cause constipation? (+3 tips)

In this article, we will discuss whether acyclovir can cause constipation or not, what the research suggests, what the factors affecting acyclovir-induced constipation and what to do if acyclovir causes constipation in patients taking it. 

Does acyclovir cause constipation?

Yes, acyclovir can cause constipation in some patients. Acyclovir is an antiviral medication and has its own side effects but constipation is not a commonly reported side effect of acyclovir. This means it is a rare side effect of acyclovir and most people taking this medication may not even experience it.

Acyclovir is an antiviral medication used to treat viral infections in humans such as chicken pox, shingles and herpes virus infections (1). It may cause gastrointestinal issues in some individuals. If you are taking acyclovir for a viral infection, it is advised to not discontinue the medication but to consult your healthcare provider about your condition and symptoms. 

What does the research suggest?

According to the FDA (Food and Drug Administration), less than 1% of patients taking acyclovir reported experiencing constipation (2). These effects may be observed due to acyclovir’s effect on the motility of the gastrointestinal tract (3). Delayed movement of food from the GIT may lead to constipation.

This effect may be achieved by the effect of acyclovir on the neurotransmitter called acetylcholine (4). Acyclovir’s effect on acetylcholine may affect the gut motility leading to constipation. 

Constipation in patients taking acyclovir may also occur due to dehydration. Dehydration may occur due to decreased fluid secretion caused by acyclovir. It may also be due to nausea and vomiting as both conditions may lead to dehydration.  

Acyclovir has been found to affect the electrolyte imbalance, particularly potassium and magnesium. The imbalance in these electrolytes can lead to disruption in the muscle contractions of the intestines causing constipation in patients (5).  

What factors affect acyclovir-induced constipation?

Here are some factors that may contribute to acyclovir-induced constipation.

Individual sensitivity

The effects of drugs may differ in different individuals. Not every patient experiences the same intensity and frequency of side effects.  Some individuals may experience constipation after taking acyclovir while it is not necessary that the same side effect may appear in every individual.

This variation in effects is attributed to the genetic predisposition of individuals, metabolic rate, gender and age of the patient.

Dosage and duration

Higher doses not only lead to higher therapeutic effects but also increase the intensity of side effects as well. Your body may show a higher incidence of side effects at the starting time of the medication as the body is trying to adjust to the effects of the drug. Once the body adjusts well, the side effects such as constipation may subside without any additional help.

Higher and prolonged use of acyclovir can cause an increased risk of constipation in patients taking it. 

Concurrent medications

Certain medications, when taken together with acyclovir, can increase the risk of developing constipation in patients taking acyclovir for any viral infection. Such medications may include the following:

  • Opioid pain medication
  • Antacids
  • Iron supplements
  • Certain antidepressants

You need to tell your doctor if you are taking any of this medication already so that your doctor can consider these before prescribing your treatment plan.

Underlying medical conditions

Individuals with preexisting health conditions are more susceptible to experiencing constipation after taking acyclovir. Such medical conditions may include the following:

  • Irritable bowel syndrome
  • Chronic constipation
  • Inflammatory Bowel Disease
  • Diverticulitis
  • Gastroparesis
  • Neurological conditions such as Parkinson’s disease.

Open communication with your healthcare provider is essential in order to get an effective treatment plan and reduce the risk of side effects.

Dietary factors  

A change in diet while on acyclovir can lead to constipation. A diet low in fibre content can also cause constipation. The patients taking acyclovir need a diet rich in fibre content to avoid constipation as a side effect of acyclovir.

What to do if acyclovir causes constipation?

Acyclovir can cause constipation in some patients. However, the incidence is rare. If you are taking acyclovir and experience constipation, then you need to consult your healthcare provider in order to address your concerns. 

Consulting health care professional

Your doctor will perform a careful analysis to determine the exact cause of constipation. It may be due to dietary factors or some underlying health condition as well. In some cases, concurrent medications may also be responsible for it. 

If acyclovir is found to be the cause of constipation, then your doctor may lower the dose of your drug or just the starting dose as it will help your body adjust better to the effects of acyclovir. Adjusting the dosage regimen can help lower the severity of the effect of the drug.

To manage acyclovir-induced constipation, your doctor may prescribe some over-the-counter medications such as (6):

  • Docusate sodium
  • Osmotic laxatives
  • Bulk-forming laxatives
  • Lubricants

However, if the symptom does not subside even after the adjustments in the treatment plan then your doctor may recommend switching to an alternative medication that will be equally effective in treating your condition but with a lower risk of constipation.  

Alternatives to acyclovir

If acyclovir is causing constipation or any other side effect that interferes with your routine and daily activities then your doctor may prescribe you one of these alternative medications that will help you with your viral infections. The alternative may include (7) (8):

  • Valacyclovir
  • Famciclovir

How to manage acyclovir-induced constipation?

Here are some things to manage acyclovir-induced constipation.

  • You need to eat a fibre-rich diet. Your diet should have at least 25-35g of fibre content. The major sources of fibre can be fruits, vegetables, whole grains etc. 


  • Keep yourself hydrated. 8-10 glasses of water per day are necessary.


  • Processed food must be avoided as it can worsen the symptoms. 


  • Probiotics can help with the microbiome and reduce the incidence of constipation.


  • Magnesium citrate can help draw water into the stool and help the patient with constipation. 


  • Regular exercise for at least 30 minutes maintains your normal body functions and regulates bowel movements properly.


In my opinion, acyclovir can cause constipation even though it might be a rare case. Acyclovir is an antiviral medication and for a safe and effective treatment, open communication with your healthcare provider is crucial.

They can help you with your condition and make a suitable treatment plan tailored to your needs after considering all the conditions and medication the patient is taking already. You can manage constipation with over-the-counter medications and household remedies while taking acyclovir.

This can increase the therapeutic effect of the medication and lower the incidence of side effects.  

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