Decriminalising drugs in Victoria will help end the state's "greatest public health policy failure", a specialised treatment service says.
Reason Party leader Fiona Patten will introduce her decriminalisation bill to the Victorian upper house on Wednesday.
Under the changes, police would issue a mandatory notice and referral of drug education or treatment to those found to have used or possessed an illicit drug.
If a person complies with the notice, there will be no finding of guilt and no criminal record.
Patrick Lawrence, chief executive of addiction, mental health and legal services hub First Step, said the bill would ensure those struggling with addiction - who were often targeted by Victoria's drug laws - received help rather than condemnation.
"We're talking about adults who survived childhood traumas, childhood abuse and neglect, homelessness, poverty, and the absence of love," he said.
"Most of us would move mountains to prevent harm occurring to a child. At what age (is) an adult ... no longer worthy of our compassion?"
Baden Hicks, a recovered drug addict, said criminal charges and penalties only caused further trauma.
"A drug addiction is like having a broken leg," he said.
"The criminal justice system comes along and breaks my arm trying to teach me not to break my leg again."
He said treatment had turned his life around and provided an avenue to employment.
"I work in the sector now because I truly believe it works," Mr Hicks said.
The Royal Australian College of General Practitioners has also backed decriminalising drugs, saying a health-first approach is paramount.
Similar reforms were introduced in Portugal two decades ago.
Ms Patten said Portuguese drug users were now older and using substances more safely, which led to fewer accidental-overdose deaths.
The Andrews government and state opposition have said they will not support Ms Patten's bill, which is set to be debated next month.
The upper house MP said she would continue to have "positive" conversations with both sides of the political aisle.
But Ms Patten believes the lack of support from the major parties is a result of the November state election.
"They're motivating each other. No one wants to have a law and order election, or maybe they do. So they are hoping that they can wedge each other," she said.
"This needs bipartisan support. If we look at other measures that we have pushed through this house - like safe-access zones, supervised injecting rooms, voluntary assisted dying - we started from a position where no one wanted to support it to a position where everyone supports it."