Advocacy group Doctors for Refugees says Manus Island detainees have been allocated a dangerous amount of medication.
The detainees, refugees and asylum seekers who tried to reach Australia by boat, are all men who have been held for four years without trial.
Australia is closing its Papua New Guinea detention centre at the end of the month and the detainees have been told they will be moved to three buildings in nearby Lorengau town.
Healthcare provider International Health and Medical Services (IHMS) said the men were being assisted to self-manage their medication during the transition to new accommodation.
But Doctors for Refugees president Barri Phatarfod said dispensing four weeks worth of drugs to suicidal men was risky.
"One of the most common ways that people have tried to take their own lives in the detention centres has been by swallowing things," said Dr Phatarfod.
"In the past people have swallowed razor blades, shampoo, detergent, bleach. And now they've got potentially hundreds of tablets just handed to them with no instructions when they're already depressed and suicidal," she said.
"To us it's akin to saying 'here's a gun and here's the bullets, don't do anything silly.'"
Dr Phatarfod said some of the detainees were taking up to 50 different pills each day including psychopharmaceuticals.
Two detainees who died this year on Manus Island are believed to have committed suicide.