i don't know about hair transplants, but maybe I can expalin why there's weightgain from propecia. Reducing DHT in the body generates an extra release of testosterone. Aromatase is the enzyme that catalyzes the conversion of androgens (androstenedione, testosterone) to estrogens. It also is found in certain areas of the brain in high concentration (often in conjunction with 5-alpha reductase).DHT and estrogens often run side by side
In men testosterone is also the primary substrate for the synthesis of estradiol (a potent estrogen). In normal physiological levels estradiol production does not produce noticeable changes to the physique. However when testosterone levels become exaggerated due to heavy supplementation, it may potentially increase the deposition of body fat, tissue fluid retention and possibly stimulate the growth of female breast tissue (gynecomastia). When athletes use testosterone in moderate amounts these side effects are typically not noticed. Again however, their possibility does place a limit on the dosing of testosterone without some form of ancillary drug to combat these side effects. For this reason testosterone is often used as a base in a steroid cycle, to be stacked with agents less apt to convert to estrogens.