Valacyclovir (Valtrex) and acyclovir (Zovirax) are antivirals for the herpes family of viruses. They treat cold sores, genital herpes and shingles. This page shows how they differ.
At a glance
| Valacyclovir | Acyclovir | |
|---|---|---|
| Type | Oral antiviral | Oral antiviral |
| How it works | A prodrug that your body converts to acyclovir, then stops the virus from copying itself | Stops the virus from copying itself |
| Used for | Cold sores, genital herpes, shingles | Cold sores, genital herpes, shingles |
| Form | Tablet | Tablet |
| How fast it works | Works best when started early | Works best when started early |
| Common side effects | Headache, nausea, tiredness | Nausea, headache, diarrhea, tiredness |
| Pregnancy | Tell your clinician before use | Tell your clinician before use |
| Monitoring | Kidney checks if you are at risk | Kidney checks if you are at risk |
Doses and length of treatment are set by your clinician.
How each works
Both medicines stop the herpes virus from copying itself. This does not cure the virus, which stays in your body. It can shorten an outbreak, ease symptoms and, when advised, lower the number of outbreaks.
Acyclovir is the older medicine. Your body absorbs it only in part, so it is taken more often through the day. Valacyclovir is a prodrug of acyclovir. Your body absorbs it well and converts it. This lets you take fewer doses to get the same effect.
Which may suit whom
Valacyclovir may suit you if you want a simpler schedule. Fewer doses a day make it easier to start fast and keep to the plan. This matters for cold sores, where early treatment counts.
Acyclovir may suit you if cost matters most, or if your clinician prefers it for your situation. It has a long safety record. Taking it more often can be harder for some people.
Your clinician checks that your sores really look like herpes. Your clinician also asks about kidney disease, a weak immune system, pregnancy, breastfeeding and every medicine you take.
Safety
Most people have few effects. Nausea, headache and tiredness can happen. Drink enough fluids.
Do not use either one if you had an allergy to acyclovir or related antivirals. Tell your Care Team about severe stomach pain, confusion, much less urine, or a rash with swelling of the face or throat.
Get urgent care for a shingles rash near the eye, a severe headache with a stiff neck, or confusion.
Can they be used together?
No. Valacyclovir turns into acyclovir in the body, so taking both doubles up the same drug. This raises the chance of side effects with no extra benefit. Take only the one your clinician prescribes.
Some people use an antiviral cream with a tablet for cold sores, but this is a clinical choice.
Cost and coverage
The cost depends on the medicine, the dose and your pharmacy. Each consultation costs CA$175.
Generic versions may cost less than brand names. Provincial drug plans and private insurance may cover part of the cost, and some plans need a special authorization form. Your Care Team can help with the form. See our insurance page.
Next step
Share your symptoms and history with Modern Dermatology. A Canadian-licensed medical professional will review them and tell you which option, if any, is right for you.
