Valacyclovir is an antiviral medication that’s used to treat certain viral infections, including herpes simplex virus and varicella-zoster virus (which causes chickenpox and shingles). It’s a prodrug, meaning it’s converted into the active drug acyclovir after being absorbed into the body. While valacyclovir is generally well tolerated, some people may experience side effects when taking it. One common question is whether valacyclovir can make you feel sick.
How valacyclovir works
Valacyclovir works by stopping the virus from replicating. It does this by preventing the virus from making an enzyme called DNA polymerase that it needs to replicate its genetic material and spread. Without this enzyme, the virus can’t make copies of itself or infect new cells.
Valacyclovir is converted into acyclovir in the body. Acyclovir then blocks DNA polymerase, halting viral replication. This helps shorten the duration of symptoms and speed healing.
Common side effects
Like all medications, valacyclovir can cause side effects in some people. Many of the side effects are mild and temporary. According to the product labeling, the most common side effects of valacyclovir are:
- Headache
- Nausea
- Stomach pain
- Vomiting
- Dizziness
- Tiredness
These side effects are usually mild in intensity. Only about 1-2% of people in clinical trials stopped taking valacyclovir due to side effects.
Can it make you feel sick?
Yes, valacyclovir can sometimes make people feel sick. Nausea and vomiting are two of the most common side effects.
In clinical trials, nausea occurred in up to 9% of people taking valacyclovir for herpes labialis (cold sores). For genital herpes, nausea occurred in up to 6% of people.
Vomiting was less common but still occurred in around 1-4% of people in trials.
So while most people tolerate valacyclovir well, nausea and vomiting do occur in a small percentage of users.
Why it causes nausea
It’s not entirely clear why valacyclovir causes nausea and vomiting in some people. A few possibilities include:
- Conversion to acyclovir – The conversion process in the body may form some intermediary products that provoke nausea.
- Interaction with stomach lining – Valacyclovir may interact with receptors in the stomach in a way that induces vomiting.
- Central nervous system effects – Valacyclovir or acyclovir may have effects on the brain that lead to nausea.
More research is needed to determine the precise mechanisms behind valacyclovir’s nausea side effect.
Risk factors
Certain people may be at increased risk of nausea and vomiting with valacyclovir. Risk factors include:
- Taking high doses – The risk may increase with higher dosages.
- Kidney impairment – Decreased kidney function can lead to higher drug levels and more side effects.
- History of nausea with medications – Some people are prone to nausea with medications.
- Taking on an empty stomach – Taking valacyclovir without food can worsen nausea.
- Elderly age – Older adults may be more susceptible to nausea.
Table 1 summarizes the risk factors for nausea with valacyclovir:
| Risk Factor | Reason |
|---|---|
| High doses | Higher drug levels in the body |
| Kidney problems | Decreased drug elimination |
| History of medication nausea | Individual susceptibility |
| Taking on empty stomach | More direct stomach irritation |
| Older age | Decreased tolerance |
Timing of nausea
Nausea and vomiting can occur at different times after taking valacyclovir:
- Early nausea – Within the first 1-2 hours after a dose. This may be from direct stomach irritation.
- Delayed nausea – 2-6 hours after taking it as the body absorbs and converts it.
- Next-day nausea – Some people feel nauseated the morning after taking valacyclovir, likely due to accumulation in the body.
Paying attention to when nausea occurs can help identify the potential cause. Talk to your doctor if nausea is persistent or affects your ability to take your medication.
Duration of nausea
For most people, nausea from valacyclovir is transient and may last anywhere from a few minutes to several hours. Vomiting episodes are also generally short-lived.
In clinical trials, nausea typically got better within a day or two of starting treatment. Taking valacyclovir with food may help minimize stomach upset. Staying well hydrated and resting can also help alleviate symptoms.
However, some people may experience more persistent nausea that doesn’t seem to improve with time. If nausea lasts more than a few days or keeps recurring, contact your doctor. They may adjust the dosage or switch you to a different medication.
Tips to prevent nausea
Here are some tips that may help reduce the chance of nausea when taking valacyclovir:
- Take it with food – Eat a meal or snack when dosing to buffer stomach irritation.
- Stay upright – Remain upright for 30-60 minutes after taking it to keep the medication down.
- Lower dosage – A lower dose may be better tolerated.
- Avoid irritants – Don’t take valacyclovir right after drinking coffee or alcohol.
- Take at night – Taking it just before bedtime can help you sleep through nausea.
- Pre-medicate – Your doctor may recommend pre-medicating with an antiemetic drug.
Table 2 summarizes tips to prevent nausea with valacyclovir:
| Prevention Tip | Details |
|---|---|
| Take with food | Food buffers stomach irritation |
| Stay upright | Helps keep medication down |
| Lower dosage | Better tolerated than high doses |
| Avoid irritants | Coffee or alcohol can worsen nausea |
| Take at night | Sleep through potential nausea |
| Pre-medicate | Antiemetic drugs prevent nausea |
When to see your doctor
Contact your doctor if you experience:
- Severe nausea or repeated vomiting episodes
- Dehydration symptoms from vomiting like dizziness or dark urine
- Inability to keep the medication down
- Nausea lasting more than a few days
- Signs of allergic reaction like rash, itching, or swelling
Your doctor can provide guidance on alleviating side effects. They may adjust the dosage, switch medications, or prescribe anti-nausea medication.
Conclusion
Valacyclovir can cause nausea and vomiting in some people who take it. Around 1-9% experience these side effects. The nausea is usually mild and temporary, often resolving within a day or two. Taking valacyclovir with food, staying hydrated, and using a lower dosage can help prevent nausea in many cases. Contact your doctor if nausea is severe, persists beyond a few days, or prevents you from taking your medication. With some adjustments, most people can take valacyclovir without significant stomach upset. Be sure to weigh the benefits of treatment against any discomfort from side effects.