Common side effects include nausea and diarrhea. Potentially serious side effects include kidney problems and low platelets.Greater care is recommended in those with poor liver or kidney function. It is generally considered safe for use in pregnancy with no harm having been observed. It appears to be safe during breastfeeding. Aciclovir is a nucleoside analogue that is similar to guanosine. It works by decreasing the production of the virus’s DNA.