Let's get the technical stuff out of the way first. Last August I received a shot of Lupron for a medical condition. One use of Lupron medication (usually administered via a shot by a urologist) is to shrink the prostate gland. The shot can be sized for one-month, three-months or four-months in duration. (It also can be administered by mouth on a daily basis.) Lupron works by stopping the production of sex hormones – testosterone for prostate shrinkage. Testosterone is fuel to the prostate, thus when the fuel supply is cut off, the prostate shrinks. Lupron is not like Spironolactone, or other androgen suppressors, which just inhibit the effects of testosterone, not the production of testosterone. Since Lupron stops the production of sex hormones, the production of estrogen is also shut-down. (Males produce small amounts of estrogen, just not as much as females do.) Without sex hormones, the libido goes into hiding.
As an added "bonus," hot flashes and night sweats are a daily (hourly!) occurrence while Lupron is in the system. I am not sure what mechanism causes the hot flashes and night sweats, but to this lay girl's way of thinking, I would go for the lack of estrogen (since it is the lack of estrogen in menopausal women that causes the flashes and sweats). But the medical profession states it is the lack of testosterone (in males) that creates the flashes and sweats. Once the Lupron wears off, the hot flashes and night sweats disappear and the libido returns to normal; or at least to what it was before the shot was administered. (As an aside, Lupron is also used to "chemically castrate" pedophiles.)