The suspension was backdated to May 1, so Cilic will be able to return to the circuit on January 31 and the ITF says it believes the Croat did not take the stimulant deliberately.
Cilic tested positive for nikethamide, a stimulant, in Munich.
The ITF says an independent tribunal found that Cilic "ingested the nikethamide inadvertently as a result of taking the Coramine glucose tablets, and did not intend to enhance his performance in doing so."
Cilic has not played since withdrawing from Wimbledon in June.