Tetracycline is a very strong chelating agent. It binds just about anything and takes it out of the game. When on it, docs recommend using additional birth control (other than the pill) cause it binds the estrogen (or progesterone dep on the pill). It can also decrease the effectiveness of many other drugs.
That being said, Im not sure if it will bind androgenic hormones or hinder 'gains' in any way. The PDR made no mention of its specificity. I would go with the anecdotal evidence like what Mac said. Its the best source of info.