I mean, you can be close-minded if you want to, but an individual taking a substance that the body produces to keep them within the normal, NATURAL range, is natural. Let's just look at some of the many definitions of natural to help explain the way I'm seeing this:
*being in accordance with or determined by
nature (are you within natural levels? you're natural.)
*implanted or being as if implanted by nature
: seemingly inborn (again,
are you within natural levels? you're natural.)
*having an essential relation with someone or something
: following from the nature of the one in question (is there an essential relation between health males and the normal physiological range of testosterone? Yep. Are you within natural levels? You're natural.)
*having a normal or usual character (Is a male having a normal testosterone level considered normal and usual? Well, that's actually how the define the "normal" range, so yes.)
*closely resembling an original
: true to nature (Again, are you within the normal physiological, natural range? Natural.)
*based on the state of things in nature; constituted by nature (Getting pretty obvious and repetitive here, huh?)