Decapeptyl injections contain the active ingredient triptorelin, which is a type of medicine called a gonadorelin analogue. It’s similar to a natural hormone called gonadotropin releasing hormone (GnRH). GnRH acts on the pituitary gland in the brain, causing production of testosterone in men and oestrogen in women.
Triptorelin acts the pituitary gland in the same way as natural GnRH. It initially increases the production of testosterone and oestrogen, but with continued treatment it desensitises the pituitary gland. This stops the production of testosterone in men and oestrogen in women.
The growth of most prostate cancers is stimulated by testosterone. Triptorelin deprives the tumour of testosterone, which causes it to stop growing or shrink.