Valtrex side effects — what people don’t always get told

Valtrex (valacyclovir) works well for herpes, but it can cause side effects you should know. Some are mild and easy to manage. Others are rare but can be urgent, especially if you have kidney problems or take other medicines. This page gives clear, practical info so you know what to watch for and when to call your doctor.

Common, usually mild effects

Most people notice a few simple symptoms in the first days of treatment. Expect possible headache, nausea, stomach pain, dizziness, or tiredness. These often fade after a short time. Taking Valtrex with food and drinking water can cut down on nausea and dizziness.

If a mild symptom bothers you, don’t double the dose to finish faster. Talk to your prescriber about dose changes instead.

Serious problems and who’s at higher risk

Pay attention if you have kidney disease, are elderly, or take other drugs that hit the kidneys. Valtrex is cleared by the kidneys, so reduced kidney function can let the drug build up and cause bad effects. Signs of kidney trouble include much less urine than usual, swelling in legs, or sudden weight gain.

Neurological issues can show up when levels get too high: confusion, agitation, hallucinations, tremors, or seizures. These are more likely in older adults and people with kidney impairment. If someone becomes suddenly confused or hard to wake, get emergency help.

Allergic skin reactions are rare but serious. Look for a spreading rash, blisters, mouth sores, or peeling skin. Severe reactions such as Stevens-Johnson syndrome or toxic epidermal necrolysis are uncommon but need immediate medical care.

Other rare but important risks: blood problems (like low platelets), severe allergic reactions with breathing trouble, and very rarely disorders like thrombotic microangiopathy. If you bruise easily, have unexplained bleeding, or shortness of breath, contact a clinician right away.

Drug interactions matter. Medicines that affect kidney function (NSAIDs, some blood pressure drugs), and drugs like probenecid can change Valtrex levels. Tell your doctor about all prescriptions, supplements, and over-the-counter meds.

If you’re pregnant, planning pregnancy, or breastfeeding, check with your provider. They’ll weigh the benefits and risks and decide whether Valtrex is right for you.

Quick tips: keep hydrated, follow dosing exactly, and get kidney tests if your doctor recommends them. Don’t stop suddenly if you have questions—call your prescriber to discuss safe changes.

Need urgent help? Stop taking Valtrex and go to emergency care for severe rash, breathing problems, sudden swelling, little or no urine output, or major changes in mental state. For milder issues, schedule a prompt call with your clinician to review symptoms and adjust treatment if needed.