Secoisolariciresinol, a lignan in nettle root displayed a modest inhibitory effect on DHT binding to SHBG in vitro, theoretically resulting in greater concentrations of free DHT in serum and in local tissues. The lignan 3,4-divanillyltetrahydrofuran, also present in nettle root was able to completely inhibit DHT from binding to SHBG, yet another indication that it can result in increased free (active) DHT available to tissues such as that in the scalp.
Planta Med. 1997 Dec;63(6):529-32.
Lignans from the roots of Urtica dioica and their metabolites bind to human sex hormone binding globulin (SHBG).