Acyclovir is an antiviral medication commonly used to treat viral infections caused by the herpes simplex virus (HSV) and varicella-zoster virus (VZV). While it is generally considered safe and well-tolerated, like any medication, it can have potential side effects. However, there is limited evidence to suggest that acyclovir causes any lasting damage.

According to the Drug Patent Watch website, which provides information on pharmaceutical drugs, there is no mention of any lasting damage caused by acyclovir [1].

The Drugs.com website lists several possible side effects of acyclovir, including nausea, vomiting, diarrhea, headache, and dizziness. These side effects are usually mild and go away on their own. However, in rare cases, more serious side effects such as allergic reactions, kidney problems, and neurological effects like confusion or hallucinations may occur. It is important to note that these severe side effects are uncommon and usually resolve once the medication is discontinued [2].

Valacyclovir, a prodrug of acyclovir, is another antiviral medication used to treat similar viral infections. The Healthline website mentions potential side effects of valacyclovir, which are similar to those of acyclovir. These include headache, dizziness, nausea, and stomach pain. It also states that serious side effects are rare but may include kidney problems and neurological effects [3].

In conclusion, while acyclovir and its prodrug valacyclovir can have side effects, there is no strong evidence to suggest that they cause any lasting damage. Most side effects are mild and temporary, and serious side effects are rare. It is important to discuss any concerns or questions about medication side effects with a healthcare professional.

Sources:
[1] Drug Patent Watch: https://www.drugpatentwatch.com/p/tradename/ACYCLOVIR
[2] Drugs.com: https://www.drugs.com/sfx/acyclovir-side-effects.html
[3] Healthline: https://www.healthline.com/health/drugs/valacyclovir-tablet-side-effects