What effects can 'laughing gas' have on the performance of professional footballers?
By Lyall Thomas
Last Updated: 07/12/18 7:31pm
Four Arsenal players were caught on camera inhaling what was allegedly nitrous oxide - or 'laughing gas' - from balloons.
Mesut Ozil, Pierre-Emerick Aubameyang. Alexandre Lacazette and Matteo Guendouzi will be among those spoken to by the club and "reminded of their responsibilities" after the footage emerged in The Sun newspaper.
They are not the first Premier League stars to be filmed doing balloons - inhaling nitrous oxide is not against the law - but what are the physical effects of this drug? Can it impact on the performance of professional sportsmen?
John Brewer, who is a professor of applied sport science at St Mary's University and a former head of human performance at the FA, says the long-term effects of nitrous oxide are not conducive to the work-rate required of a top-level footballer.
He told Sky Sports News: "Long-term usage can reduce the level of vitamin B12 in an individual. Vitamin B12 is essential for nerve function.
"So if you are a top-level footballer trying to make skilful movements and pass a ball effectively, you don't want your nerves to be damaged in any way because you need that peripheral ability to sense movements.
"We also know that long-term use can cause a condition cause anaemia, which is where your haemoglobin level drops. Haemoglobin is the part of the blood that carries oxygen from the lungs to the working muscles.
"If you have lower ability to do that, it impacts on your endurance and ability to recover, and your ability to perform short, sharp, explosive bursts of activity - so, again, not conducive to the work-rate we would expect to see in a professional footballer."
Nitrous oxide is legal to possess, but it is illegal to give away or sell it to others. It can give users a feeling of euphoria or calmness, and can also lead to fits of laughter - hence its nickname of 'laughing gas'.
However, inhaling nitrous oxide can also cause headaches, dizziness and even paranoia.
Players including Raheem Sterling and Kyle Walker have previously been caught on camera inhaling laughing gas.