i was on the injection for a year and a half and was 'on' constantly, only lightly but it was very annoying. think i only went 3months on the trot with no period. the same thing happend to my mate but then i know someone whos been on it for 8years and never had a period. it just varies with different people
I've been on the 'depo' injection for 7.1/2 years now and never ever have periods unless I have to take antibiotics, I do think everyone is different but if it suits you it is a very good method, I would recommend it.
It's a great contraception. I've used it for almost 6 years (did have about 18months off it at one point when I was a bit broody...) and never had a 'proper' period. Doctors are supposed to warn you that if you do use it for a long time it can increase the risk of osteoporosis though...