Acyclovir is an antiviral medication that is used to treat infections caused by the herpes virus, including genital herpes, cold sores, and shingles. While acyclovir is generally considered safe and effective, it can cause some side effects, some of which may be serious.

The most common side effects of acyclovir include nausea, vomiting, diarrhea, headache, and dizziness [2]. These side effects are usually mild and go away on their own within a few days. However, if these side effects persist or become severe, it is important to contact a healthcare provider.

In rare cases, acyclovir can cause serious side effects, including allergic reactions, kidney damage, and neurological problems [1]. Signs of an allergic reaction may include rash, itching, swelling, severe dizziness, and trouble breathing. Symptoms of kidney damage may include changes in urination, swelling in the ankles or feet, and fatigue. Neurological problems may include confusion, hallucinations, seizures, and tremors.

It is important to note that these serious side effects are rare and usually occur in people with underlying health conditions or who are taking high doses of acyclovir for an extended period of time [3]. Therefore, it is important to follow the dosage instructions provided by a healthcare provider and to report any unusual symptoms to a healthcare provider immediately.

In conclusion, while acyclovir is generally considered safe and effective, it can cause some side effects, including nausea, vomiting, diarrhea, headache, and dizziness. In rare cases, acyclovir can cause serious side effects, including allergic reactions, kidney damage, and neurological problems. Therefore, it is important to follow the dosage instructions provided by a healthcare provider and to report any unusual symptoms to a healthcare provider immediately.

Sources:
[1] https://www.drugpatentwatch.com/p/tradename/ACYCLOVIR
[2] https://www.drugs.com/sfx/acyclovir-side-effects.html
[3] https://www.webmd.com/drugs/2/drug-941/acyclovir-oral/details