While warnings are not specifically listed on the product label, it is best to avoid alcohol consumption when taking the prescription drug Valtrex. It is possible for alcohol to reduce the effectiveness of the medication and to worsen side effects such as dizziness, warns Mayo Clinic.
Patients are also advised not to combine Valtrex use with drugs that potentially harm the kidneys because this results in an increased risk of kidney damage. This includes other antiviral drugs, cancer medicines, arthritis or pain medicines, intravenous antibiotics, lithium and methotrexate. To lessen symptoms, begin treatment immediately at the onset of tingling and burning, before the appearance of sores or lesions.