Salem, Oregon - Three years after becoming the first state to decriminalize all drugs, Oregon has reversed course, making possession of even small amounts an offense again.

Governor Tina Kotek on Monday signed a law that will provide for up to six months in prison for anyone caught with hard drugs like fentanyl, heroin, cocaine, or ecstasy, starting in September.

The reversal ends a three-year experiment that left police officers handing out $100 fines and cards with details on how users could get treatment for their addictions.

The plan was to treat drug use as an illness, rather than a crime, and was modeled on rules in other jurisdictions like Portugal, where decriminalization has been in place for two decades.

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But the change coincided with a boom in the use of fentanyl – a potent synthetic opioid that has claimed tens of thousands of lives in the United States through overdoses.

Critics say Oregon was too slow to establish the treatment centers it needed as part of its two-pronged approach to decriminalization.

The result was an explosion of unabashed drug use on city streets, resulting in sometimes fatal overdoses on sidewalks and in parks.

As the death toll grew, public opinion turned against the plan, and the state's left-leaning politicians reversed course.

But Kassandra Frederique, executive director of the Drug Policy Alliance, on Tuesday criticized the U-turn. She said it "abandons a health approach and reverts to the failed approach of treating drug possession as a crime."

"It’s a false promise of change that will cycle people through the criminal legal system with no meaningful connection to treatment," she added.