Tamoxifen mimics the effects of estradiol on food intake, body weight, and body composition in rats.

Treatment of ovariectomized rats with the nonsteroidal antiestrogen tamoxifen mimicked the effects of estradiol and caused significant decreases in food intake and body weight. The decreases in body weight were reflected mainly in a decreased body fat content, although tamoxifen treatment did suppress linear growth too. Similar to the effects of estradiol, tamoxifen decreased parametrial white adipose tissue wet weight and lipoprotein lipase activity. When given concurrently with estradiol, tamoxifen showed no evidence of antiestrogenic activity on any of these measures. As reported previously, tamoxifen acted as a partial agonist/antagonist for uterine weight. The effective dose of tamoxifen for suppression of food intake, body weight, and body fat content fell between 10 and 50 micrograms/day. Therefore, tamoxifen behaves like other nonsteroidal antiestrogens and mimics but fails to antagonize the actions of estradiol on many aspects of physiological and behavioral regulation of energy balance.