The use of snus stimulants are "big" in English football, Stoke midfielder Charlie Adam says.

Adam's opinion came amid reports of the growing use of snus in the game, and after the Football Association reiterated its commitment to warning players of the dangers of legal highs.

Snus are nicotine pouches that are ingested by placing it between the top lip and the gum. They are not a banned substance in the sport, though it is illegal to buy in the United Kingdom.

England and Leicester striker Jamie Vardy admitted using the product in his autobiography and was pictured carrying it at Euro 2016. And according to Adam, plenty more have joined him, as a Daily Mail report had earlier claimed.

"It's big in the game, not just Premier League, League One, League Two, Championship, Scotland..." he told BBC 5 Live. "It's come in from Scandinavia really and a lot of the players are using it.

"There are different strengths. It's the 'in' thing. I've never tried it -- I don't know what it means -- but I've seen lads do it. I see lads every day take it. It's the norm at the moment in the game.

"It's not for helping performance. Some managers are probably taking it as well, I don't know. It's out there and that's the way it is."

Manchester City boss Pep Guardiola said earlier in the day that his players have been briefed by the club doctor in response to reports on snus, which is believed to provide a mental and physical boost.

"The doctor spoke about that this morning. I didn't know about it," Guardiola said. "The doctor spoke with the players. I don't know the benefits or pleasure about that. I only knew about that this morning when the doctors came in my office and talked about that.

"They spoke with the players but I don't know [what they said]. I was preparing the training session. I did not have a further explanation.''

Vardy openly admitted using "snus" and claimed in his 2016 book "Jamie Vardy: From Nowhere, My Story" that some players used it during games.

"Doing everything by the book has never been my style," he said. "When I joined Leicester I started using snus, which are nicotine patches that you place against your gums, for 10 minutes or so.

"I used to have the odd fag on a night out at Fleetwood, but one of the lads introduced me to snus when I signed for Leicester and I found they helped me chill out.

"A lot more footballers use them than people realise, and some lads even play with them during matches.''

An FA spokesperson said on Friday: "The FA's comprehensive national anti-doping programme fully complies with the World Anti-Doping Agency (WADA) code, which identifies those substances prohibited in and out of competition.

"As well as combining research and testing to uphold and preserve the integrity of the sport, a key part of the FA's anti-doping programme is to safeguard the physical health and mental well-being of players through a wide-ranging education package.

"This includes warning them of the dangers presented by 'legal highs', not prohibited by the WADA code."

The EFL is also compliant with the FA's anti-doping programme.