Need help obtaining documentation for card

My friend just got an appointment with a doctor to discuss the possibilites of obtaining a club card. The reason my friend gave for needing the card was that he's anorexic (and he is) and it helps him eat. He was hospitalized not too long ago and had to visit a psychologist for his eating disorders.

The doctor he is meeting up with isn't his normal doctor, but they asked for him to bring in documentation of his incident. How would he go about doing that? Should he get documentation from the emergency room he was sent to? Or the psychologist? Both?

Anything........when I had to bring my documents in for my appointment,I had to bring in anything from a doctor that said "Chronic Back Pain" So I had to get a letter from my chiropractor and I also got some things from my old doctor....One thing is,Its better to have too much documents than not enough....