"Crude marijuana extract competed with estradiol for binding to the estrogen receptor of rat uterine cytosol. Condensed marijuana smoke also competed with estradiol for its receptor. Pure delta 9- tetrahydrocannabinol, however, did not interact with the estrogen receptor. Ten delta 9-tetrahydrocannabinol metabolites also failed to compete with estradiol for its receptor. Of several other common cannabinoids tested, only cannabidiol showed any estrogen receptor binding. This was evident only at very high concentrations of cannabidiol. Apigenin, the aglycone of a flavinoid phytoestrogen found in cannabis, displayed high affinity for the estrogen receptor. To assess the biological significance of these receptor data, estrogen activity was measured in vivo with the uterine growth bioassay, using immature rats. Cannabis extract in large doses exhibited neither estrogenic nor antiestrogenic effects. Thus, although estrogen receptor binding activity was observed in crude marijuana extract, marijuana smoke condensate and several known components of cannabis, direct estrogenic activity of cannabis extract could not be demonstrated in vivo.
MA Sauer, SM Rifka, RL Hawks, GB Cutler and DL Loriaux "
This makes some sense to me, not all MJ will increase estrogen levels. If you took pure THC there would be no estogen. In most studies i think they use pure THC, which would explain no estrogenic effect.
So Apigenin and other phytoestrogen in marijuanna, that have no pyschotropics effects, are probally the cause of increased estrogen.