What are Valtrex (valacyclovir) side effects? 

The most common adverse reactions of Valtrex are listed below. Tell your doctor if these side effects are severe or if the adverse effects persist.

• Headache
• Upset stomach
• Stomach pain
• Vomiting
• Diarrhea
• Constipation

Some of the adverse effects of Valtrex are more serious and require immediate medical attention. Call your doctor without delay if you have the following serious symptoms:

• Rash, itching
• Fever
• Confusion
• Yellowing of the skin or eyes
• Blood in the urine

The above list may not include all the potential side effects of Valtrex. Talk to your doctor if you have severe side effects or if they do not improve over time. You can also report unusual side effects to the Food and Drug Administration at 1-800-FDA-1088.

Valtrex Overdose: In case of a known or suspected overdose, call your doctor or pharmacist immediately, call your local poison control center, or call the national helpline at 1-800-222-1222. If a person has collapsed, had a seizure, has trouble breathing, or cannot be awakened, call 911 immediately.

Source: FDA