PREGNYL 1500 is to inject 1500-3000 I.U. every 4th or 5th day, for a duration usually no longer than 2 or 3 weeks. If used for too long or at too high a dose, the drug may actually function to desensitize the Leydig's cells to luteinizing hormone, further hindering a return to homeostasis. Timing the initial dose is also very crucial. If your were coming off a cycle of Sustanon for example, testosterone levels in your blood will likely stay elevated for at least 3 to 4 weeks after your last injection.