Hi,
I would say that having sex will not affect how the hormones work. The hormone treatment stops the production of the male hormone testosterone which feeds the cancer, this causes the PSA to fall which is a good indicator if the treatment is working. Your dad should be having his PSA checked regularly and if it stays low this should reassure him that his hormone treatment is working.
Many men cannot have sex if they are on hormone treatment as they cannot achieve an erection, or suffer loss of libido and are no longer interested in sex. This could be the case with your dad, and he may be to embarrassed to say to your mum and just uses the hormone treatment as an excuse. I am not saying this is the case, but it could be.
If you want to talk to someone about this, please call the free number at the top of this page and speak to one of the specialist nurses. They are absolutely brilliant and will be able to answer any questions you may have, they will not rush you and will talk to you for as long as you need.
Regards,
Gerry