Thank you both for your replies. It didn't seem likely to me that it would be a reason for exclusion either, but I read that other conditions which also are not infectious, so far as we know (such as schizophrenia) are a reason for exclusion, but I guess that's because of the worry that a patient in psychosis might not be able to give their full informed consent(?)
Anyway, thank you; I'm more confident now that I'll be able to register.

Its because the medication for schizophrenics contains lithium, a strong addictive that would be noxious to people who aren't schizophrenics.