The injections aren't there to take away periods. That's just a side effect. They're supposed to stop you getting pregnant. Mind you, as you say, they seem to achieve their contraceptive effect mainly by inhibiting the sex drive The 'usual' contraceptive pill has the same effect as this injection because both of them work by convincing your body you are actually pregnant. You are, however, supposed to stop the pill once a month for a few days which means you get a period albeit one you can sometimes time to suit your requirements...

Before the advent of effective drug based contraception, the only way to stop a period was by getting pregnant. There are records which indicate that many women often only had a few periods (before they got married) before spending most of their life pregnant.

I have no qualms about sex during a period or even oral sex during a period (after all, it doesn't affect her ability to suck... Ok, bad chauvanist humour there... ). Seriously, it does not bother me at all to go down on a woman who is having a period. Maybe it is the fact that I used to work with human blood a lot which means I am innured to it? Maybe it is because I am part vampire? I have, however, heard tales of men whose manhood 'fainted at the sight of blood'. Something about the process turned them off in some way which they had no control over.

The different reactions to the process from women is evidence that we are all affected by hormones in often quite radically different ways. It is not surprising, given that pretty much every cell has steroid hormone receptors and often these receptors vary (in number and type) between cell type to cell type and even person to person.