How are "research" chemicals legal (Pharmaceutical Grade)?

There's alot of wierd crap on the internet. It seems that some daredevils have cirvented the laws regarding pharmacies and pharmaceuticals (that require Rx), and have brazenly begun selling pharmaceutical grade chemicals in "research" form (no tablets or clear method of administration, just the chemical in liquid form). I specifically encountered "research" versions or Tamoxifen, Clomid, and Arimidex when I was researching steroids. Bodybuilders use these to either prevent the aromatization of the androgens they abuse or block estrogen receptors from being activated. I would like to better understand the premise under which these "research" forms of pharmaceuticals can be sold legally. It is absolutely bizarre.