They should be prescribed by a doctor or mental health professional; however, there are also websites that "sell" certificates/letters. 

Just see if your Doctor can make a "house call".

It sounds like the person is already a tenant and if that's the case, you can ask for credentialing, such as a Doctor’s note to validate and verify if it’s a legit medical need, if you cannot confirm the need then you can deny the accommodation. 

Numerous new buildings in this industry have popped up over the last year which is going to lend itself nicely to mid-term and long-term rentals for traveling nurses, doctors, etc.

Doctors are QuacksLawyers are crooksPriests are pedifilesUsed car Salesmen are a jokereal estate sales agents are weasels. politicians are fraudsAnd of course contractors are Cons.We live in such a wonderful and trusting World nowadays don't we?

@Alex Gaeta I'm not a doctor, but thanks for telling me about it.

Back in the 80's, with interest rates of 13% or more, we even managed to cash flow very well.Similarly, she purchased several rentals with her son, a doctor, put $50k each back in the 80's, 90's and each is worth $1.0 million plus, as SFR in San Francisco all passed the one million threshold 10 years ago, in the crazy market there, and I'm told they're all mortgage free right now.She also bought one SFR with her youngest daughter.Counting everything up, from 1980, when her husband died, when she's 60 years of age, with the $600K on hand, no job and in retirement, I counted up conservatively, $5 million returns between her and her children here in NY and San Francisco.