National leader Simon Bridges today said that his party would abide by whatever decision the referendum returned.
But Clark would not commit to that.
"I'm not ruling that in or ruling that out but it's too soon to say because I haven't had that conversation with colleagues."
Bridges said legalising cannabis was not the answer to the problem of synthetic cannabis but National would abide by whatever the outcome was.
"We've got to go with what the people want," he said.
Cabinet is seeking urgent advice over the spike in deaths linked to the use of synthetic cannabis use.
Provisional figures from the Coroner show that up to 45 people had died through using synthetic cannabis in the year to June, compared with only two deaths in the previous five years.
The Ministers of Health, Justice, Police and Customs are seeking urgent advice on how to reduce the number of deaths.
Acting Prime Minister Winston Peters yesterday acknowledged that the Government, and previous governments, hadn't come up with solutions that have worked.
Clark said today it was deeply concerning that the number of deaths had spiked.
"We need to know as ministers whether there are other things we can do that will work more immediately to address the issue," he said.
"Those who peddle these drugs need to face the full force of the law, I agree with that, but none of them are peddling drugs thinking they are going to be caught at the moment, and that's one of the concerns."
Synthetic drugs were constantly being reformulated and it was difficult to keep up with what was on the market but reclassifying them was being reconsidered, Clark said.
Police Minister Stuart Nash said it was difficult to know what was in them.
"The thing about synthetic is you just never know what's in it. So it's everything from people in their back sheds with grass clippings and flyspray rolling stuff up to stuff that's being imported.
"People are dying because we don't know what's in this stuff."
Nash said a "Pandora's Box" had been opened when synthetic cannabis was legalised.
"Now what we need to do is deal with the situation in front of us and that is, Kiwis are dying, and we need to figure out how we're going to deal with this. A lot of the people who are dying are often the most disaffected and disenchanted, disengaged, so its not just a matter of running a advertising campaign on the news. There are other strategies we need to put in place," he said.