Hi Thanks for your query As cold sores you are getting are not that bad so lysine is good choice for it, as it prevents the virus from growing somehow, usually it is safe but in very few cases of kidney problems have been shown with it rarely. You should obviously consult a specialist if you have kidney problem before continuing lysine. Now coming on to your query Yes, oral antivirals are prescribed for cold sores but they have little effect after the sore has developed. They may reduce the severity or duration of symptoms. They are also useful in improving pain and initiate the healing process but cannot totally eradicate this virus. If you are having frequent and severe outbreaks then antivirals can prevent the recurrence if taken regularly. Yes every medicine, if taken for long duration, have some adverse effects. Kidney issues have been reported in case of some antivirals. Other effects like insomnia , nausea , vomiting, allergy, diarrhea etc have also been reported. If your cold sores are not very severe then you can use zinc oxide topical cream it may reduce the duration of outbreak somehow. Regards