The appointment of former HSE chief executive Paul Reid has been criticised by Green Party TD Patrick Costello.
The Dublin South Central called the appointment of Mr Reid as a "missed opportunity" campaign to randomly select the members of the public to join the Citizens Assembly will begin this week.
The Citizens Assembly has the potential to recommend a radical shake-up of Ireland's drug policy, a proposal long backed by the opposition.
Speaking after his appointment by the Taoiseach, Mr Costello said he thinks it was a "poor appointment".
"It's a poor appointment for many reasons. One of them is that the fact is the HSE is a major deliverer of drugs services,"Mr Costello said.
"Now that's not anything against the HSE, but I think we need to have outside thinking and fresh eyes on this. I think it's a missed opportunity to bring in somebody fresh, to bring in somebody with fresh ideas, fresh thinking and creativity, to this huge problem"
Minister of State for public health Hildegarde Naughton, who has responsibility for drug policy, said they want to find out who is exactly taking drugs in this country.
"What we want to do to the Citizens Assembly is really pull back the veil of the real use across all sector of society.
"We have people who are highly functioning, who take drugs, and I think that's one of the areas that's going to become visible as the Citizens Assembly start their work.
"People might have a picture of who takes drugs, who is addicted to drugs, and I think this will unveil the real realities."
