Caffeine has also been proven to slow and even stop the replication of DNA, which leads to lower sperm counts.
A Caffeine Overdose is classified as taking more than 250 mg in a 10-30 minute period, though this can change depending on body mass. An overdose of caffeine can result in nausea, vomiting, numbness in the fingers or toes, confusion, drowsiness, convulsions, and possibly death.
-Information from WebMD, and Caffeine FAQ