Elaine Smith, mother: "I don't think Nick saw it as a risk"
The family of a teenager who died after taking mephedrone has called on the government to make the drug illegal.
Louis Wainwright, 18, and Nicholas Smith, 19, died in Scunthorpe on Monday after taking the drug.
Tony and Elaine Smith said they believed their son would not have taken mephedrone if it was illegal.
A fourth person has been arrested on suspicion of supplying drugs to the teenagers. Three people held on Tuesday remain in police custody.
Mr Smith said he thought his son had been unaware of the dangers of mephedrone.
He said: "I assume that because it's a legal drug he thought it was safe to take. I am convinced he took it because it was legal, why would anyone assume it could kill you?
The teenagers' families have paid tribute to them
"He would be alive if the ban was in place."
Mrs Smith, who is a nurse, said: "He certainly wasn't a regular user, there was no changes in Nick whatsoever, he was just his usual happy..in fact he was at the time of his life when he was exceptionally happy.
"And he was doing well at work and, you know, he certainly wasn't to the best of our knowledge he wasn't taking any drugs on a regular basis."
Mr Wainwright and Mr Smith were found collapsed at their homes after a night out in Scunthorpe.
Police believe they had been drinking and had also taken another drug, the heroin substitute methadone.
At a news conference, Dt Ch Insp Mark Oliver said: "A mixture of any type of drug, including alcohol, increases the likelihood of anyone coming to harm."
Mr Oliver said it would be weeks before toxicology tests could determine the cause the the teenagers' deaths and whether mephedrone was a contributory factor.
The drug is known by various names, including "M-Cat", "MC", "mieow", "meow", "4MMC" or simply plant fertiliser.
Det Ch Insp Mark Oliver, from Humberside Police: "Four men have been arrested"
The teenagers' families have paid tribute to them through police.
A statement from the Smith family said: "Nick was a dearly-loved and precious son and brother who brought joy into the lives of all who met him.
"He was a hard-working, normal boy, training as a chef, with a bright future in front of him, which has been tragically cut short.
"He was fun-loving, with a wonderful sense of humour, which will sadly be missed by all who knew him."
Mr Wainwright's mother Jacqui said he was a "fun-loving and caring boy who would do anything for his family and friends".
"He had a fantastic personality, he was always somebody who made people laugh and was a popular lad," she added.
Mrs Wainwright said her son was working hard towards a career in engineering.
She added: "The family are completely devastated by our loss. He was such a lovely boy, he was loved by many people."
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