You need to check if the person providing the service is a 'practitioner' as defined by Revenue.
This is the link to the Irish Medical Council Register.
Acupuncture - My reading of the below is that you can only claim if it was carried out by the GP themselves.
(or the person providing service is on the Register)
Psychological services - it depends on the qualification of the person providing the service.
treatment from a psychologist or psychotherapist where either: the psychologist or psychotherapist is a practitioner
or you are referred for a diagnostic procedure by a practitioner
Consultants - no GP letter needed as they are 'practitioners' themselves, if they are on the medical council register.