Acyclovir is an antiviral medication that is commonly used to treat herpes simplex virus infections. While it is generally considered safe and effective, like any medication, it can cause side effects in some people.

According to the drug patent watch [1], the most common side effects of acyclovir include nausea, vomiting, diarrhea, and headache. These side effects are usually mild and go away on their own within a few days. In rare cases, acyclovir can cause more serious side effects such as seizures, confusion, and hallucinations. These side effects are more likely to occur in people with kidney problems, as acyclovir is primarily eliminated from the body through the kidneys.

Medical News Today [2] reports that other less common side effects of acyclovir can include dizziness, fatigue, and skin rash. It is important to note that some people may be allergic to acyclovir, and can experience symptoms such as hives, difficulty breathing, and swelling of the face, lips, tongue, or throat. If you experience any of these symptoms, seek medical attention immediately.

The Children's Hospital of Pittsburgh [3] notes that acyclovir can also interact with other medications, so it is important to inform your healthcare provider of all medications you are taking before starting acyclovir. Additionally, if you are pregnant or breastfeeding, you should discuss the risks and benefits of taking acyclovir with your healthcare provider.

In conclusion, while acyclovir is generally considered safe and effective for treating herpes simplex virus infections, it can cause side effects in some people. The most common side effects include nausea, vomiting, diarrhea, and headache, while more serious side effects are rare. It is important to inform your healthcare provider of any medications you are taking and to seek medical attention immediately if you experience any symptoms of an allergic reaction.

Sources:
[1] https://www.drugpatentwatch.com/p/tradename/ACYCLOVIR
[2] https://www.medicalnewstoday.com/articles/acyclovir-side-effects
[3] https://www.chp.edu/our-services/transplant/liver/education/medications/acyclovir-zovirax