I am not sure if this applies to everyone, but when dicussing my weight gain with my GP, she said that both the pill and the injection contain a hormone that makes you hungry, and thus, many, many women gain weight whilst using this mode of contraception. My GP also said that the Implant is completely different, it doesn't release the same hormone, and because it releases the hormones over a very long period of time, you're getting a very steady dose, where as with the injection and pill, it drops off and then, BAM! When you take another or get it again, it spikes again. Like I said earlier, the fact that the G[ said it has no impact on weight gain/loss, is the reason I chose it.