While other parts of the world are decriminalising cannabis, South Australia plans to quadruple fines and introduce prison terms.

The South Australian Liberal party ran a "war on drugs" slogan in April, and today it delivered on that election promise, announcing new laws to be debated in Parliament this week.

The proposals include:

A maximum fine for cannabis possession of $2,000 plus a two-year jail term

A cap on the number of times a person can enter a drug diversion program - an alternative to prosecution, designed to address drug use through education and counselling - of twice in four years.

Allowing drug-sniffing dogs into schools.

Attorney-General Vickie Chapman told the ABC the changes would make the penalty for possession of marijuana the same as for heroin.

"This is a serious drug and those who have previously said it was a recreational drug, not much worse than tobacco, really those days are over," she said.

'A war on the poor'

Critics say the proposals are empty virtue-signalling that will clog up the courts and discriminate against the poor and the vulnerable.

The Law Society of Australia said the proposed laws would effectively divert people from counselling and education and into the prisons.

Dr David Caldicott, who is the clinical lead to the Australian National University's Australian Medicinal Cannabis Observatory, said harsher penalties do not decrease use of marijuana, or the incidence of harm.

"Maybe it's to generate revenue," he told the ABC.

"The likeliest scenario for its purpose is to send a message to those who support these policies - it's a form of virtue-signalling."

Greens MLC Tammy Franks said the penalties were "a war on the homeless, Aboriginal people and the poor" who were least able to afford to defend themselves in court.

Changes follow murder inquiry

The weed crackdown stems from an inquiry into the murder of 18-year-old Lewis McPherson by 17-year-old Liam Humbles in 2012.

McPherson was shot dead outside a party in Adelaide by Humbles, who had consumed alcohol, taken ecstasy and smoked cannabis that day.

Humbles had undergone five drug diversion programs relating to drug possession.

The deputy coroner, Anthony Schapel, recommended a limit to the number of diversions a young person could undergo.

He also called for an increase in the maximum cannabis possession fine.

Cannabis possession has been decriminalised in South Australia since 1987. If passed, the SA bill would overturn three decades of cannabis policy in the state.