PRECAUTIONS: See also Side Effects section.Before taking valacyclovir, tell your doctor or pharmacist if you are allergic to it; or to acyclovir; or if you have any other allergies. This product may contain inactive ingredients, which can cause allergic reactions or other problems. Talk to your pharmacist for more details.Before using this medication, tell your doctor or pharmacist your. Valacyclovir is an antiviral drug. It slows the growth and spread of the herpes virus to help the body fight the infection. Valacyclovir is used to treat infections caused by herpes viruses, including genital herpes, cold sores, and shingles (herpes zoster) in adults. Valtrex (valacyclovir) is an antiviral medication used to treat infections with: herpes zoster , herpes simplex genitalis (genital herpes), and herpes labialis. Valtrex is available in generic form. Find information about common, infrequent and rare side effects of Valacyclovir Oral. For the Consumer. Applies to valacyclovir: oral tablet. Along with its needed effects, valacyclovir may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention. If you have herpes, it’s extremely likely that you’ll be prescribed either valacyclovir or a similar drug in order to manage the virus. Valacyclovir is highly effective in managing herpes. It’s also an extremely safe, well studied medication. In this guide, we’ll go over what valacyclovir is, how it works and the potential side effects you can expect from using it as part of herpes. Do not share valacyclovir with another person, even if they have the same symptoms you have. Valacyclovir side effects Get emergency medical help if you have signs of an allergic reaction to valacyclovir : hives; difficult breathing; swelling of your face, lips, tongue, or throat. Valacyclovir does not prevent the spread of herpes. To lower the chance of giving genital herpes to your partner, do not have sexual contact during an outbreak or if you have symptoms. Side Effects. Drug information provided by: IBM Micromedex. Along with its needed effects, a medicine may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention. Q: Does Valtrex have any side effects that I should be concerned about over the long-term? I'm currently taking it for a first-time outbreak of herpes and don't know yet if I will have to take it.