THE public drinking ban may have caused an increase in drug use in indigenous communities, according to a report.

The claim was expressed in anecdotal evidence collected by the City of Yarra over a three-month period, as part of a report to gauge the local impact of the 24-hour public drinking ban, known as local law eight.

The report's findings prompted the Greens party to withdraw their support for the 24-hour drinking ban at the latest council meeting, an outcome that has raised doubts about the future of the law.

According to the report, since the law was introduced three months ago the 'parkies' - a group that gathered on Smith street, Collingwood - has split into smaller groups to assemble in different locations.

This included a move to areas in Richmond and Fitzroy where drugs such as heroin were freely available, the report said.

"There is a reported increase of substance use by some of the Parkies," the report said.

The dispersement of the community has made it difficult for agency workers to locate individuals, according to the report.

"The Neighbourhood Justice Centre Aboriginal liaison officers have stated that they had 100 per cent attendance for court appearances before [the public drinking ban] was introduced. This rate has dropped because the officers cannot contact the Parkies like they used to."

Council has given $30,000 to drug and alcohol centre Turning Point to conduct an independent evaluation of the law to be completed by August.

The law will be further debated at a council meeting on April 20.

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