Speaking from an Australian perspective and only as an donor in any way...
There are many things that can disqualify you from being a donor. These are based on the risk they present to the recipients of the donor material. That is why they are interested in male-male sexual practices, drugs use (needles), piercings (including electrolysis and tattoos). Single use needles for piercings and electrolysis are apparently OK but I haven't tested the proof requirements. They don't like anyone here who was in the UK during the mad-cow scare a few years ago but I am not sure if it disqualifies you.
Medications are another area where they have to be very careful. Finasteride is a no-no as it is very dangerous to females. Aspirin is another because of its anti-clotting characteristics - imagine giving donated blood products to someone who has low clotting factor and needs more blood! HRT itself (excluding Finasteride if that is in this bucket) should be ok as the amounts of hormones shouldn't impact a recipient - it would be like going on E for a day!
On another point, don't be possessive about your blood. Turning it over every now and then doesn't harm the donor at all and saves lives. Saving it is really pointless, in my opinion. Here, whole blood can be donated every 3 months, plasma every 2 weeks and platelets monthly (it is a plasma donation at the same time). Having done all 3 in the past, I would like to get back to the 2-weekly plasma/platelets cycle.
As they say in Australia, 1 in 3 Australians will need blood donation products, 1 in 30 donate. That is the problem especially for rare blood types. The Red Cross in Australia also maintains the register of bone marrow donors. If in doubt, phone them and ask and if you are eligible, give it a go!
