The sanction was announced on Tuesday at the end of anti-doping processes held by Sport Integrity Australia and the NRL, and is backdated to the start of his provisional suspension on December 1.
The NRL released a statement saying the penalty is in line with new provisions of the incoming World Anti-Doping Code 2021, which has slashed penalties for cocaine use provided the athlete can establish it was used out of competition and was unrelated to sport performance.
"Having established that the ingestion of the cocaine was out-of-competition and not for performance enhancing purposes, Naden is sanctioned in accordance with new provisions of the incoming World Anti-Doping Code 2021 which permit a one-month period of ineligibility for qualifying athletes who also undertake an approved rehabilitation program," the NRL said.
"The sanction will come into effect on 1 January 2021 with the commencement of the new WADA Code."
The NRL said the penalty only related to the anti-doping breach and the 24-year-old outside back could face further sanctions, with the matter to be reviewed in the new year.
Naden entered a rehabilitation facility in Sydney to deal with drug and alcohol issues after fronting Panthers staff in the days following the grand final loss to Melbourne, admitting recreational drug use.
The Panthers said they continued to support Naden, who was "working through his personal issues".
"Our club acknowledges the penalty handed to Brent Naden by the NRL in relation to his use of a recreational drug," said Panthers boss Brian Fletcher.
"Brent has come to understand the significant impact of his actions on his family, our club and the game of rugby league.
"He similarly understands how fortunate he is to have the opportunity to return to the NRL in 2021."
The club said Naden would be back at pre-season training next week.