Side effects of finasteride include impotence (1.1% to 18.5%), abnormal ejaculation (7.2%), decreased ejaculatory volume (0.9% to 2.8%), abnormal sexual function (2.5%), gynecomastia (2.2%), erectile dysfunction (1.3%), ejaculation disorder (1.2%) and testicular pain. Resolution occurred in men who discontinued therapy with finasteride due to these side effects and in most of those who continued therapy. In December 2008, the Swedish Medical Products agency concluded a safety investigation of Propecia and subsequently advised that the use of Propecia may result in irreversible sexual dysfunction. The Agency's updated safety information lists difficulty in obtaining an erection that persists indefinitely, even after the discontinuation of Propecia, as a possible side effect of the drug.
Once you're in, your medical needs are managed by the Army. Repeat prescriptions included. If your taking it now, and need to continue taking it then (as long as it isn't a bar to entry) you need to tell them so you can still get hold of it!
If it is a bar to entry, and you can't discontinue using it, then other employment must be saught, I'm afraid.
IIRC, they will ask you, at some point in the process, for your permission for them to access to your civilian medical record. I am not aware what happens if you refuse (I assume they put a hold on your application.)
It's prescription: declare it - if you don't you can drop yourself right in the brown and sticky.
Go to your doctor and ask him/her if it will be a drama during your application. (Every time I see my CivQuack I check whether I need to notify the Medical Officer on camp.) If there are any dramas your doctor should be able to advise you in advance of any possible dramas. You could get a letter from your doctor listing all the meds, dates, symptoms, etc, etc, of your case and take it to your medical.
Some health centres/practices charge for a medical form, Â£10 - Â£15, if you ask the reception staff to get the doctor to sign what they've filled out.
Book an appointment to speak to your doctor about any concerns you've raised on here, then hand him the form and say could I have that in writing? Might get it done for free but he can also then be more specific with the form and hopefully stop you having to go back again and again.