The head of Italy's Senate blocked the anticipated legalisation of a weaker form of cannabis, in a last-minute reversal.

Parliament, while approving an amendment to the 2020 budget last week, okayed the legalisation of cannabis products containing less than 0.5% of the psychoactive compound THC. 

But in passing the budget early Tuesday, the president of the Senate, Maria Elisabetta Casellati, declared the amendment "inadmissible" on technical grounds. 

Casellati, who is a member of the centre-right Forza Italia party, said the decision was not politically motivated. 

"If you think this measure is so important for the majority, then propose a bill," Casellati told members of the Five Star Movement (M5S), which rules in a coalition with the centre-left Democratic Party (PD).

Some 4,000 hectares (9,884 acres) of land are planted with cannabis in Italy.  

The decision cannot be appealed.