630,000 people signed a petition calling for the cultivation of the plant to be decriminalised.
A referendum on making growing cannabis legal in Italy has been blocked by the country's constitutional court.
In a ruling on Wednesday, judges said the law would have forced Italy to violate its international obligations to prevent drug trafficking.
But critics said that the court had stifled the democratic process after a petition gained 630,000 signatures, well above the threshhold to trigger a referendum on the issue.
It came on the same day that the constitutional court also denied a referendum on euthanaisa, the petition for which received over 750,000 signatures.
Benedetto Della Vedova, secretary of the centrist party + Europa, said the court had "deprived Italy of a public debate and an electoral process for reforms on freedom and responsibility."
Supporters of the referendum believed that the legalisation of cannabis, which they say is no more harmful than legal substances such as alcohol and tobacco, would have made it possible to remedy overcrowding in prisons while focusing police action on violent criminal organisations.
Currently, the cultivation of cannabis plants incurs a sentence ranging from two to six years in prison, despite the fact that since 2016 possession of small amounts of the drug has not been a criminal offence.
Opponents of the referendum project, including Matteo Salvini and the leader of Fratelli d'Italia, Giorgia Meloni, have argued that decriminalisation could encourage the use of other drugs.
It is a blow for legalisation and decriminalisation advocates in Europe, which has seen a number of European states - including Spain, Germany and Italy - ease penalties for possession of the drug.
The decision comes just weeks after Malta became the first European country to legalise both the possession of small amounts of drug and the cultivation of up to four plants at home.
The island nation acted to prevent low-level cannabis users being dragged through the courts - and, in the case of cannabis growers, jailed - and suffering economic hardship as a result.
Owen Bonnici, the minister responsible for the law, told Euronews that Europe should follow Malta's example in an interview last week.
“We were hearing and meeting people and telling us stories after story and experience after experience. I’m being honest: I would be looking at them and completely at a loss about what to tell them. I heard stories of people who literally passed through hardship because of, I don't know, four grams of cannabis,” he said.
“You realise that if you want to make a difference to people’s lives, you have to take bold decisions.”