How long does acyclovir take to start working?
For most people, acyclovir begins to affect the virus fairly quickly after it’s taken, but the noticeable clinical improvement usually comes after a short delay. The exact timing depends on the condition being treated (for example, cold sores vs. genital herpes vs. shingles) and the dose/formulation.
How fast do cold sores improve after taking acyclovir?
For cold sores (herpes labialis), people often notice changes within about 1–2 days of starting antiviral treatment, especially when treatment begins early (ideally at the first tingles or sore onset).
How fast does it work for genital herpes?
With genital herpes, symptom improvement commonly takes a bit longer than cold sores. Many people see reduced pain, fewer new lesions, or faster healing within a few days after starting acyclovir, with the full course taking longer.
Does acyclovir work faster if you start early?
Yes. Antivirals work best when started as early as possible in the outbreak. Starting at the first signs (tingling, burning, itching, or early lesions) can shorten the time to healing more than starting after the outbreak is well established.
What changes should you expect and when?
Typical signs that treatment is helping include:
- New lesions stop appearing or appear less frequently
- Pain and burning start easing
- Existing sores begin drying/crusting or healing
If symptoms are not improving after several days of treatment (or are worsening), that’s a reason to contact a clinician for advice on whether the diagnosis, timing, or dosing needs adjustment.
When should you seek urgent help?
Get prompt medical care if you have severe symptoms, fever, signs of eye involvement (pain/redness or vision changes), significant immune suppression, or complications. These situations may require different dosing or urgent evaluation.
Sources
No external sources were provided with your question, so I did not cite any. If you tell me which acyclovir product you mean (pill vs. topical cream vs. IV) and what infection you’re treating (cold sores, genital herpes, shingles), I can give a more specific time window.