Although the use of nutritional supplements by adult athletes has been extensively studied, information on supplements consumption by adolescent athletes is still limited. The present study reports on the use of nutritional supplements contaminated with banned doping substances among 170 recreational adolescent athletes from eleven, randomly selected, gym centres, in Athens, Greece. Nutritional supplements consumption was reported by almost 60% of the study population, with proteins/amino acids and vitamins being the most popular. Nine per cent of the users were found to consume nutritional supplements contaminated with anabolic steroids, prohormones, selective androgen receptor modulators (SARMs) and aromatase inhibitors, all pharmacological substances with endocrine modulating properties not stated on the label. None of these individuals had previously consulted a physician or a nutritionist. A representative sample (ca 15%) of the protein/aminoacids and creatine preparations used by the study population were also tested and found free from doping substances. The majority (63%) of adolescents purchased products from the internet. In conclusion, exercising adolescents can have easy access to contaminated nutritional supplements and “black market” products, which could constitute a risk for public health. Low level of awareness and low involvement of medical care professionals among recreational adolescent athletes is also observed. Display omitted •Almost 60% of recreational adolescent athletes in Greece use nutritional supplements.•Nine per cent of the users were found to consume nutritional supplements contaminated with doping substances.•Contaminations were pharmacological substances with endocrine modulating properties not stated on the label.•Protein/aminoacids and creatine preparations tested were found free from doping substances.