One hundred and forty drug users have already been treated for potentially fatal overdoses at Melbourne's safe injecting room, according to its medical director.

Key points: 140 drug users have been treated for potentially fatal overdoses at the facility

140 drug users have been treated for potentially fatal overdoses at the facility The injecting room's medical director says the trial has been a success

The injecting room's medical director says the trial has been a success Construction on the planned purpose-built injecting room will begin in coming weeks

Since the controversial trial began two months ago, the North Richmond Community Health Centre has received 8,000 visits, with some users coming to the centre multiple times a day.

Medical director Dr Nico Clark told ABC Radio Melbourne that the number of emergency call outs attended to by the health centre had been reduced since the safe injecting room opened.

"It's working very well, it is doing exactly what it intended to do, we are seeing increasing numbers,'' Dr Clark said.

He said while it was "too early" to tell if there had been an overall reduction in medical responses to overdose, he was confident there had been a drop in the number of incidents in North Richmond.

"Certainly there appears to be less sirens going during the day,'' he said.

Mental Health Minister Martin Foley, whose portfolio is charged with tackling drug abuse, said there had been 140 overdoses at the centre in the first two months which could have been fatal had they happened on the street.

"This was [set up] to save lives, every indication is this facility is saving lives," Mr Foley said.

The Opposition says it will scrap the trial if it wins the state election. ( ABC News: Michael Barnett )

After initially resisting calls for the centre, including from within his own cabinet, Premier Daniel Andrews last year backed the trial in the heroin hotspot near Victoria Street.

More than 30 people died in the area over a 12-month period, and last year the coroner called for a trial.

Residents in the area were also behind the plan in the hopes of stopping addicts shooting up in their front yards, streets and in laneways.

Dr Clark said the centre was often full. On Thursday there were 211 visits.

He conceded there had been some aggressive behaviour, but said that was expected given the challenges faced by some users, including mental health and homelessness.

Dr Clark said the centre's first two months proved there was a need for expansion.

Centre 'sending wrong message' to kids

The trial is legislated to last two years, with an option for a third.

It has been operating out of the existing community health centre in North Richmond while plans are made for a purpose-built facility.

The Andrews Government today revealed construction would begin on the new facility in the next few weeks.

Mr Foley said the new building would provide more counselling and treatment rooms, and more capacity for treatment and support services.

But the Opposition, which has seized on the location of the centre next to a primary school, has promised to scrap the trial if it wins the November election.

The school has worked with the centre and is supportive of the trial.

Opposition MP Tim Smith told ABC Radio Melbourne he was sceptical about the results, questioning the doctor's independence from government.

"I'll wait and see what a statistical analysis provides," he said.

Mr Smith said the centre was sending the wrong message to school children.

"We're simply shifting criminal activity from one part of Richmond to another," he said.

"These people are breaking the law, they're injecting drugs right next door to a primary school and I think the messages that sends to young children is disgraceful."

The Opposition has also railed against the decision to allow ice users at the centre.

Dr Clark said 98 per cent of drug use at the centre was heroin, with one per cent of patrons using ice.