Gonadorelin is synthetic gonadotropin-releasing hormone, a ten amino acid signal produced by the hypothalamus that instructs the pituitary to release the hormones which in turn drive testosterone and oestrogen production. It was historically an approved medicine in the US under names including and Lutrepulse, used diagnostically to assess pituitary function and therapeutically in certain fertility contexts, and some of those products were later discontinued commercially. It remains widely used in veterinary medicine and in endocrinology. In fitness communities it is marketed as a testosterone restart, which is a use it was not approved for and which conflates it with hCG, a different hormone acting at a different point in the pathway.