Suprefact is a trade name for Buserelin Acetate. This med effects the pituitary gland and is used for certain hormone responsive cancers. There are some side effects you may be concerned about, such as other hormone imbalances, like an increase in testosterone. Also, FSH and LH will be effected. Initially you get an increase in these two hormones, but with long term use, your body becomes less sensitive to the effects of these hormones.
In my opinion, as long as you do not have any other issues besides gender dysphoria, Suprefact would not be my first choice as an Antiandrogen. Spironolactone or Finasteride are much more commonly used for this purpose.