Less serious side effects that may be more likely to occur can include:
Nausea, vomiting, diarrhea, decreased appetite, or abdominal pain; a headache or lightheadedness; or joint pain.
Full list of possible side-effects of Valtrex:
General: Anaphylaxis (a life-threatening type of allergic reaction), angioedema (swelling similar to hives), fever, headache, pain, peripheral edema (abnormal buildup of fluid in the ankles, feet, and legs).
Nervous: Aggressive behavior, agitation, ataxia (loss of coordination), coma, confusion, decreased consciousness, delirium (severe confusion), dizziness, dysarthria (disturbance of speech), encephalopathy (degenerative brain disease), hallucinations, paresthesia (burning, prickling, tingling, or creeping on the skin), psychosis (irrational thoughts and fears), seizure, somnolence (drowsiness; sleepiness), tremors. These symptoms may be marked, particularly in older adults or in patients with renal (kidney) impairment.
Digestive: Diarrhea, gastrointestinal distress (upset stomach and intestines), nausea.
Hematologic and Lymphatic: Anemia (a lower than normal number of red blood cells), leukocytoclastic vasculitis (a condition that causes inflammation of the small vessels), leukopenia (abnormally low white blood cell count), lymphadenopathy (swelling of the lymph nodes), thrombocytopenia (when the number of platelets [a type of blood cell] is abnormally low, sometimes associated with abnormal bleeding).
Hepatobiliary Tract and Pancreas: Elevated liver function tests, hepatitis, hyperbilirubinemia (elevated levels of bilirubin within the blood), jaundice (yellowing of the skin and eyes).
Musculoskeletal: Myalgia (muscle pain)
Skin: Alopecia (loss of hair), erythema multiforme (a skin disease that causes lesions and redness), photosensitive rash (sensitivity to light), pruritus (itching), rash, Stevens-Johnson syndrome (a severe allergic reaction that can result in skin blistering, fever, and eye damage. It is potentially fatal, and can also cause blindness and disfigurement), toxic epidermal necrolysis (a life-threatening skin disorder characterized by blistering and peeling of the top layer of skin), urticaria (hives).
Special Senses: Visual abnormalities.
Urogenital: Renal failure (kidney failure), elevated blood urea nitrogen, elevated creatinine, hematuria (blood in the urine).
Detailed information about the side-effects of VALTREX® (Valacyclovir)