Valtrex Side Effects and Interactions

Valtrex may cause mild or more serious side effects that, depending on their severity, will either need to be reported to your doctor or watched closely until they go away. Any signs of an allergic reaction to Valtrex, such as swelling of the tongue, lips or throat, trouble breathing or hives, should be reported to the local emergency center.

Serious side effects of Valtrex are highly unlikely and can include increased thirst, trouble concentrating, swelling, weight gain, hallucinations, lower back pain, mood changes, nausea and vomiting, seizure, speech or vision problems, loss of appetite and confusion. You need to call your doctor if any of those appear. More severe side effects that require stopping the treatment and contacting your doctor immediately include bloody diarrhea, urinating less than usual, fainting, yellowed skin, easy bruising and weakness.

Mild side effects of Valtrex are more likely, although they still occur in only a few percent of patients taking the medicine. You can continue the treatment if you develop stomach pain, nausea, headache, dizziness, stuffy nose, sore throat, joint pain or mild skin rash, because those usually go away on their own without any need for your doctor's interference.