The 2013 Act banned recreational psychoactive drugs from sale or supply.
Brown has a member's bill that would increase the maximum penalty for supply from two to 14 years in prison.
"The statistics released under the Official Information Act show that in the 2016/17 year there were roughly 40 hospitalisations from synthetic drug use, and last year there were more than 80. Hospital admissions were as low as 10 in the 2015/16 year after the Psychoactive Substances Act was introduced, Brown said.
"The correlation is clear between the large increases in hospital admissions and manufacturers of synthetic drugs continually coming up with deadlier strains. Labour and the Greens continue to ignore the seriousness of this issue, and if it wasn't for New Zealand First's continued support of my Bill these numbers would likely rise again," he said.
Ross Bell, executive director of the Drug Foundation, said the Act had created a black market and it was regulation that would reduce the number of deaths and hospitalisations, not tougher penalties.
"What those numbers show is that under regulation … we didn't see the problems that we're seeing today. We certainly didn't see the deaths that we're seeing today and the Government's data shows quite clearly that hospitalisations were much lower under a regulated market," Bell said.
"We should be looking at regulation rather than tougher penalties. I don't get the leap in logic from here is a problem and if we have tougher penalties that's going to miraculously make this problem go away. I do not get [Brown's] logic."
A short-term fix that would make a difference would be enabling ambulance staff and emergency department staff who treat synthetics users to connect them with social and health services.
The Drug Foundation was carrying out research in which it was working with frontline agencies and interviewing users.
""The majority of them are homeless and are telling us they need a house. So actually, the solution doesn't lie with tougher penalties. The solution in most cases would be getting people the kind of social and health support that they need. In many cases that is getting them off the street and into stable accommodation.
The findings of the research, in which about 60 users were interviewed, would go to the Government once it was completed, Bell said.
Health Minister David Clark said the use of drugs needed to be treated as a health issue and focus on harm reduction.
"Legislating for longer penalties might feel like taking tough action, but there is no credible evidence that it would actually reduce harm," he said in a statement.
Clark said the Government was working on a considered response which involved the Ministries of Health, Justice, Police, Corrections and Customs.
Last month, Clark announced he would see Cabinet support to reclassify as Class A drugs two compounds commonly found in synthetics – AMB Fubinaca and 5FABD.
"The harm around them is well-documented and reclassifying those drugs as Class A will give police the same search and seizure powers as they have for other hard drugs that cause serious harm," Clark said.
Bell said the Government needed to get going and take action.
"It's nice you're saying those things, but actually we need action," he said.
The Drug Foundation and other health and justice agencies launched a petition last week calling on Prime Minister Jacinda Ardern to back up her call to treat drug use as a health issue and double investment for drug-related treatment and harm reduction in Budget 2019 to $300 million a year.
An independent cost benefit analysis released by the Drug Foundation earlier this month found that by investing an extra $150 million in drug-related health interventions, the social benefit for New Zealand could be at least $225m.
