SARMS RAD140 powder is indeed very interesting.
First, as to terminology. An “agonist” is a molecule which activates a receptor. A full agonist, at high enough concentration in the blood or test medium, can achieve 100% effect from the receptors. A partial agonist, also called a weak agonist, can only ever achieve partial effect from the receptors. In some cases it binds the receptors, but no activity results. In some cases, the presence of a partial agonist can reduce the effect of a full agonist that is also present. For example, in humans estriol, a weak agonist, can reduce the effect of estradiol, a full agonist.
The concept of a modulator, as opposed to being a simple agonist of some type, is that when the molecule binds to a receptor, in some tissues the receptor will act in one way and in other tissues, a different way.
Nolvadex Tamoxifen or Clomid Clomiphene Citrate. for example, cause estrogen receptors in breast tissue to work differently than when estradiol binds the receptors, but in bone tissue causes the receptors to work in the same way as when estradiol binds.
So what would be the significance to androgens? In muscle cells we’d want the molecule to work in the same way that testosterone does. But in tissues that we don’t want androgenic effect, ideally we’d want the molecule to work differently at the androgen receptor than testosterone does.
In terms of the most commonly measured effect – levator ani growth vs prostate growth* – we already had this with the synthetic anabolic steroids. The difference in effect was calculated as the anabolic/androgenic ratio. Values for this ratio reached as high as a reported 20:1 with norbolethone, 16:1 with norethandrolone, and 12:1 for Anavar Oxandrolone.
SARMS MK2866 Ostarine and some others showed anabolic/androgenic ratios comparable to this, though a little better. Differences were arguably more quantitative than being in kind or class, particularly given that the assay method gives quite variable results from one study to another.
RAD-140, however, has shown an anabolic/androgenic ratio of about 90:1, and actually antagonizes (partially blocks) the effect of testosterone on the prostate. That’s an impressive demonstration.
Now as to whether RAD-140 has less activity in the scalp or, for women, the larynx than synthetic anabolic steroids, that would be a differing question which may have a differing outcome.
It’s a very interesting compound, and could be of value as part of a steroid stack due to its partial testosterone blocking effect in the prostate.
* In the rat, the muscle sometimes called the levator ani acts to elevate the penis. While it responds differently to anabolic steroids than skeletal muscle cells in general do, in the anabolic/androgenic ratio measurements levator ani growth is used as a guess factor for general effect on skeletal muscle growth. Prostate growth provides some useful information on effect on the prostate and is used as a guess factor for effect on other tissues such as the scalp and the larynx, but is of no proven value for estimating effect on those tissues.