HALIFAX -- Prime Minister Justin Trudeau faced difficult questions from the crowd at a town hall in the Halifax area Tuesday, including from a member of the navy who has ALS and from the mother of a boy with severe autism.

A man with ALS who identified himself as the father of two young children and a member of the navy asked Trudeau why he doesn't have the right to try experimental drugs to fight his terminal illness.

"If it is my right to be able to choose death due to my terminal illness, why am I not allowed the right to try experimental drugs that have passed the Phase 1 medical study in Canada?" the man said during the question-and-answer session at a school gym in the Halifax suburb of Lower Sackville, pointing to the Charter of Rights and Freedoms section on the right to life.

"Why are my only options to die now, or wait to die, when what I want is the right to try?"

Trudeau responded by telling the man that ALS has affected him personally, noting the death of longtime MP Mauril Belanger, who he described as a friend and mentor.

"I know the challenges ahead of you," said Trudeau, as more than 1,000 people sat in grey chairs in a circle around him in what was the first of a new series of town hall meetings across the country.

He said the process of approving such drugs needs to be rigorous and based on science.

"I know there are always new approaches and new techniques that people look to with hope," said Trudeau, the sleeves of his collared shirt rolled up on his forearms.

"We have to make sure that we're going through rigorous scientific processes in terms of what is going to work and what is going to be effective."

Carly Sutherland, whose nine-year-old son Callum has severe autism and suffers from violently aggressive fits, asked the prime minister to commit to national autism strategy.

She noted the Senate has called for such a plan, and issued a report a decade ago calling for more assistance.

Trudeau acknowledged that she's not alone in her struggles, but avoided directly answering her question about a national autism strategy.

"We recognize that education and health-care delivery are very much a responsibility for the provinces. But there is more that the federal government can and is doing on the research side, on the advocacy side, and on the support side," he said.

A health-care worker also expressed his concern with the minimum age to buy recreational marijuana being set at 18, citing studies that show it can be problematic for brain development in young people. Trudeau reassured that Ottawa's plan is meant to help keep cannabis out of the hands of young people.

"We know that setting the age too high simply encourages the continuation of a black market," said Trudeau. "It's not a perfect solution -- not by any means. But it is a better solution than the one we have right now, and it's grounded in facts and science and a responsible approach to public safety and public health."

Trudeau also faced questions about his controversial Bahamas vacation, pensions for veterans, the Omar Khadr lawsuit settlement and about Abdoul Abdi, a 23-year-old former child refugee who is facing deportation to Somalia.

Earlier in the night, social media was abuzz after Trudeau appeared to refer to the United States as "somewhat unruly" during his opening remarks.

"There are people that are thinking about our place in the world and how Canada is you know, dealing with a somewhat unruly neighbour these days -- maybe unpredictable at times," a smiling Trudeau said to enthusiastic applause.

The prime minister was scheduled to be at McMaster University in Hamilton, Ont., on Wednesday afternoon. He was then heading west.