The tablets were removed from the list early last year but WADA is said to be alarmed at the increasing use among sportsmen.
WADA's announcement followed Gregan's claim that the pills boosted his performance by 7 per cent and had been approved by the Australian Institute of Sport. Several Australian Rules Football players have also admitted using caffeine tablets.
The Australian government has since said it will hand over any information it has on caffeine use to help WADA assess whether the drug should be banned.
Although there was no suggestion that anyone had broken the rules, sports minister Rod Kemp said he was concerned that high-profile athletes were taking caffeine.
"It is clear that inappropriate use of caffeine raises health issues and side effects, and it is important that athletes are well aware of these implications," he said.