The widespread use of supplements by school sports team could have dangerous consequences, says the chief executive of Drug Free Sport New Zealand.
Graeme Steel's comments come in the wake of a joint survey with the University of Otago School of Medicine into the attitudes towards supplements of 1st XV rugby teams from seven schools.
The survey examined what 142 rugby players thought about consuming nutritional supplements, their use and also delved into whether banned substances were also being taken.
Mr Steel told Nine to Noon that a worrying finding from the study was that half of the respondents would not report teammates or opposition members who were doping.
"And the findings have thrown up some major concerns about the use of such products by sporty teenagers, their access to them and the need for coaches and parents to understand the risks," he said.
"It is becoming normalised and can have dangerous consequences."
The most popular supplements were protein powders and sports recovery and energy drinks. The teens said they wanted to improve muscle size, strength, performance and recovery.
"Players just seem to take supplements because that is the thing to do rather than understanding why specifically a particular supplement may help and getting expert advice around that rather than just buying gallon after gallon of stuff that they really don't understand."
Mr Steel said the use of supplements could lead to the abuse of more detrimental products, banned drugs and steroid use, and that many elite teams, particularly 1st XVs were "under enormous pressure to perform".
School sport teams were not tested for drug use but Mr Steel said that might change.
"If future research suggests it's necessary for competitions to remain clean, that might be an option, as schools are putting more and more emphasis on the prestige of sporting success, and often a coach's pay is results linked - which may not have them taking a sufficiently holistic view of an athlete."
Mr Steel said schools and coaches needed to advise players that supplements were often contaminated and the habit could lead them to using banned substances.
The foster mother and coach of the basketball star Steven Adams, Blossom Cameron, said she had seen schoolboys in the gym who were using steroids.
"I see them in the gym and the next thing I see them walking out in their school uniforms. They don't understand that it is going to affect their reproductive organs later on in life."
She had alerted her boss to the problem in December and said one of the body builders she knew who was dealing steroids in the gym was now serving a prison sentence.