Im 16 does mass gainer stunt your penis growth ?

Protein supplement?: I am not sure what the active ingredients in mass gainer are, but my experience with otc products used for building muscle mass tells me that it is probably some sort of amino acid/protein supplement, possibly whey. If so, it is unlikely to impact your pubertal development, which is usually complete in boys by 17 years of age. If mass gainer contains any exogenous androgens, i would not use it.