This weekend is probably the last time clubbers and party goers can take mephedrone without fear of prosecution.
It is due to be reclassified as an illegal drug next week when a bill passed by Westminster gets royal assent.
BBC Scotland's health correspondent Eleanor Bradford went in search of this notorious 'legal high'.
The Commons has given its backing to a ban on mephedrone
I have been told mephedrone is everywhere.
Apparently it is now one of the most popular street drugs.
Whatever you call it - M-cat, Miaow-Miaow, or Moonshine - within a few minutes of asking clubbers on Sauchiehall Street in Glasgow, I had found a man who had taken it.
He wanted to remain anonymous.
"M-cat's attractive to people who have never taken drugs before because of its legal status, " he told me.
"It's also attractive to people of my age - 26 to 27 - who have been on the drug scene for years, who are looking for something with no known side-effects.
"You can buy it online without fear of recrimination."
Two more women admit to taking it, and dozens of others say their friends have.
So what exactly is in this new phenomenon called mephedrone?
To find out, I went to meet Dr Paul Skett, a forensic pharmacologist at the University of Glasgow, who is an expert in illegal and legal highs.
Mephedrone, he tells me, comes from Khat, a flowering shrub from Africa. Its leaves are chewed as a stimulant.
"Chemists have simply modified it - very slightly to be honest - and made a compound which appears to be much more powerful," Dr Skett said.
He is doubtful whether a ban on mephedrone is the right approach.
"I think the chemists who have been making mephedrone almost certainly have new things lined up already.
"They will just slightly change the structure again. Even if the idea is to ban all cathinones made from Khat, they will simply modify it so it's not a cathinone."
Dr Skett gives me an interesting tip. He tells me that if I want to find mephedrone I need to head for Ayrshire or Tayside, where the market is flooded with it.
The town of Ayr saw Scotland's first mephedrone-linked death, although, like all mephedrone associated deaths, no definite link has been proven.
I visited Heads of Ayr, a shop in the main shopping area which sells pipes, bongs and other drugs paraphernalia.
The owner is adamant he has never sold mephedrone and says he never would.
A customer tells me if I want mephedrone I'll need to head to a nearby back alley, to Ayr's sex shop.
Inside staff are friendly, and the owner invites me into his office.
He does not want to be named, describing himself as "the black sheep of the family" but argues his case for selling "Moonshine".
He points out that it is still legal, with no proven deaths.
He says he can guarantee his supply of mephedrone is pure and is not "cut" with other substances.
Of course, the small pills he has behind the counter come in a packet marked "not for human consumption".
He is using up the last of his stock, expecting a ban any day, which he sees as pointless.
Heads of Ayr is already selling a new legal high called Stardust, he tells me, which is much stronger.
I leave with a free sample of Moonshine, but later that evening MPs vote to reclassify it as an illegal drug, so I dispose of it down the toilet.
The end of one legal high, an opportunity for another.