Yes WW although the idea that some posters are more qualified to answer than others is the issue.
If someone want's to believe that someone has certain skills and knowledge like being a doctor, then PM is a better way in my view for many reasons.
Certainly a Christmas cracker of a thread!
No I think the best approach is to speak in person to a medical professional even about a general question.
Even then I know from personal experience they can sometimes make mistakes.
As a diabetic for a number of years I had to go on to insulin as well as oral medication. I saw a diabetic specialist nurse who explained how to inject a small dose twice daily. I found I was having hypoglycemic episodes following the injections when I consulted my GP she said "are you mixing the solution before injecting?"
I hadn't been advised about that by the specialist nurse and that was causing the hypos. The solution is made up of 30%fast acting and 70% long acting insulin if you don't mix it you can take more fast acting insulin which leads to hypos. Luckily I was only taking a small dose!
12 months later I had a heart attack it came out of the blue I have no family history of heart problems my only risk factor was diabetes. On admission to hospital the Cardiac consultant said " I'm stopping your Canagliflozin (oral drug to treat diabetes) he didn't specify why. A GP friend visited me in hospital and was shocked O'd been on Canagliflozin and insulin as the combination (she said) could cause complications. The same diabetic nurse who recommended insulin didn't take me off Canagliflozin!
In each case it took a Doctor rather than a nurse practitioner to spot the problem and resolve it!
To give proper advice you need to be a qualified and experienced professional with access to medical history and records. The OP said a photographer friend told him about prep and asked for advice from forum members who'd tried it. Seems pretty innocuous..however someone knowing his history and medications he uses should be able to provide better advice than us even if some of us do happen to be medically qualified.
But as has been pointed out the question prompted an "interesting" thread.