Plans by the Queensland government to increase penalties for cannabis possession and trafficking to match those for “harder” drugs has been described by drug policy experts as a “retrograde” and “uninformed” step.

The Queensland attorney general, Yvette D’Ath, is expected to introduce the proposed reform to the state’s anti-drug laws by the middle of the year, as part of reforms recommended in a report on the Organised Crime Commission of Inquiry.

If passed, the reforms will be introduced as Queensland prepares to hold clinical trials on the use of medical marijuana, after announcing it would join New South Wales and Victoria in potentially allowing the legal use of the drug.

The commission of inquiry report, released last month, recommended that the Drugs Misuse Act 1986 and supporting Drugs Misuse Regulations 1987 be amended to remove the distinction between schedule one and schedule two drugs. As the law currently stands, offences like trafficking for schedule one drugs – such as heroin, cocaine and methylamphetamine – carry a maximum penalty of 25 years, while the same offence for a schedule two drug – like cannabis, ketamine or morphine – carries a maximum penalty of 20 years.

The proposed changes would not affect the quantities of each drug that trigger a higher penalty.

In a report outlining its response to the commission’s 43 recommendations, the Queensland government said that removing the distinction between “hard” and “soft” drugs would simplify enforcement.

“A one-schedule drug regime will remove any risk of inconsistency in the scheduling of substances and provide for a more readily transparent penalty regime, which may enhance its deterrent value,” the government response said.

The Palaszczuk government has said it would accept 35 of the 43 recommendations in full and five in principle, with two recommendations still awaiting response. Only one recommendation, requiring all documents in drug cases to be provided in hardcopy form, was rejected outright.

Dr David Caldicott, a drug and alcohol expert from Australian National University, said increasing penalties for cannabis possession had no evidentiary basis and contradicted the advice of Australian and global drug experts.

“I’d like to know what tea leaves or entrails they divined to find the answers to these questions because it’s certainly not in the published drug and alcohol literature,” Caldicott told Guardian Australia.

“It doesn’t seem to me to be the kind of policy that any expert worth their salt would endorse.

“It’s a retrograde, uninformed, scientifically questionable, but not entirely unexpected for Australia.”

Gino Vumbaca, the president of Harm Reduction Australia, said it was wrong to suggest that the harm caused by cannabis use was equal to the harm caused by “harder” drugs like methamphetamines. For young people and Indigenous Australians, the two groups with the highest cannabis usage, Vumbaca said the risk of harm from higher penalties was greater than the risk of harm from the drug itself.

“One of the greatest harms they face is being arrested and charged,” he said. “That provides a lifelong harm for job opportunities and travel opportunities.”

D’Ath said the proposed reform would make penalties for drug offences more transparent.

“Simplifying the way illicit substances are scheduled under the Drugs Misuse Act recognises that all drugs are dangerous and pose a risk to health and public safety,” she told the Courier Mail.

“It also brings Queensland into line with other Australian states. It means courts can sentence on the basis of the ­quantity of the drug and circumstances of the offending rather than the classification of the drug itself.”

The proposed crackdown on cannabis in Queensland comes as Victoria is preparing to investigate a 20% increase in fatal heroin overdoses. Fairfax Media reports that the number of fatal heroin overdoses hit a seven-year high of 168 deaths in 2015, after causing between 127 and 137 deaths annually since 2009, prompting Victoria police and the state coroner to conduct a joint inquiry.

• This article was amended on 19 May 2016 to correct the penalty for trafficking schedule two drugs from 25 years to 20 years.