Synthetic FSH is rarely used for testosterone replacement and is typically reserved for men who have lost the ability to produce testosterone after prolonged exogenous testosterone use.

“there is also a synthetic FSH it's far more expensive and it's virtually never used so the typical use case for synthetic FSH is in men who have been on testosterone replacement therapy for many years who have now lost the ability to make testosterone because if you are given enough exogenous testosterone you will shut down the capacity to make testosterone in very short order and within a year two years you will permanently lose that ability minus some Herculean doses of synthetic LH and synthetic FSH”