herpes simplex
"I have been taking generic (cheap) acyclovir for 52 years.  I am 67 and contracted the herpes simplex while out in the sun at age 15.  Consequently, I have not been sunbathing for 52 years and look like I am 50.  There have been no side effects and I take this every day--800 mg.  When I stop, I get an outbreak.  Tried to go off it last year and had 5 outbreaks in 4 months.  So now back on.  Take it the minute I feel a tingle, 5 a day for 5 days and no  problems.  But still wear 70 sunscreen."