The union’s national performance nutritionist, Ruth Wood-Martin, said no player under 18 should use supplements such as creatine, which are widely available on the internet and on the high street.
She said the increased popularity of muscle-building products across all ages and all sports may be due to a lack of understanding of manufacturers’ claims, many of which are not backed up by scientific evidence.
“Often, the desire to get physically bigger is the reason young people choose to take supplements, which they see as a quick-fix answer for accelerated growth, but there is little evidence to condone this,” said Ms Wood-Martin.
“Young players will gain size and strength from well-planned training and recovery, supported by good nutritional practices.”
She specifically warned young rugby players to avoid creatine and said some supplements may contain banned or even harmful substances
“The IRFU strongly advises against the use of nutritional aids, in particular creatine, in young players under 18 years of age. Also, the use of protein supplements should not be recommended by schools, coaches, teachers or others involved in the training of young athletes.”
The IRFU has issued a specific set of guidelines to rugby schools and clubs, which is available from the IRFU website.
It also plans to use social media to warn teenagers such products may contain banned substances which are not stated on the label, and that their long-term safety is still unproven, particularly among young users.
“The IRFU has worked closely with the Irish Sports Council to implement an anti-doping programme at under-age level, as there is a possibility that a sports supplement may contain a banned and possibly harmful substance that a player is unaware of,” said Ms Wood-Martin.
“This could see them fail an anti-doping test or risk their health, so players must take steps to ensure they protect themselves.”
Former Ireland captain and manager Dónal Lenihan welcomed the warning.
“It’s something I would welcome. I know the use of these supplements among younger players is something the IRFU has been nervous about for a long time. I suppose the only surprise is that it has taken them so long to issue a definitive statement on it.”
Mr Lenihan said younger schools players often felt under pressure to gain muscle and size, and that this was a concern where a player may not have fully matured.
“It’s certainly a worry for a lot of parents,” he said. “Some kids grow quicker than others and the worry is they put on muscle through these products before they have fully matured.
“It’s a difficult one because young guys look up to international players, some of whom openly eulogise the products. Products like Maximuscle have been advertised in rugby magazines, by clubs, and the Lions.”
Earlier this year, chairman of Ireland’s anti-doping committee, Brendan Buckley said young athletes were playing “Russian roulette” with their health and their integrity in the sport.
“There is evidence that the use of some supplements can even be fatal,” said Prof Buckley.