Sure, you can get medical advice, but that's only based upon the information provided by the person on the other end of the communications device. If you do not possess the knowledge and continued training in the medical field(s), it would be indeed difficult to provide even the most preliminary, basic information to a qualified physician on the other end of the line. Sure, you might get lucky, but I wouldn't want to bet my life on it.
Additionally, the vast majority of pleasure craft do not have the necessary diagnostic equipment on board to even make an educated guess, let alone a definitive diagnosis. It takes an EKG machine to determine if someone is having a heart attack - otherwise you could be giving dangerous drugs to someone that merely is suffering from indigestion, and vice-versa. Most boats don't even have a simple stethoscope or blood pressure cuff onboard. How about a pulse oximeter? I didn't notice any nitroglycerine in that kit either. Treat an infection with the wrong antibiotic and you make that bug immune to not only that antibiotic, but often many others of the same ilk. Then of course, some antibiotics, when combined with others, cause C-diff, which can easily kill you - (ask me how I know this!)
I talked with Paul McElroy a few minutes ago, and he said that there are a lot of CFR subsections pertaining to this, and you have to read them all. He also said, "keep in mind that a medical doctor or PA cannot provide themselves with a prescription - it must be provided by another medical doctor or PA, and that PA has to be working under an MD. They cannot do it on their own. As for walking into a drugstore with your recreational boat's documentation papers and filling a bag with prescription drugs, Paul said "Absolutely NOT!" He also said that on all commercial vessels, the drugs are under the control of both the captain and a certified, trained medical officer. And, every drug on that commercial vessel must be accounted for, and documents containing the number dispensed, who they were dispensed to, expiration dates, and number remaining in stock must be reported annually, or upon demand by the USCG during even a routine boarding or inspection.
Paul also said that the kits that are available may have to have a prescription in some jurisdictions in order to be supplied to the consumer. I found this to be true when I ordered an oxygen generator for myself a few months ago. Keep in mind the O2 generator is not a dangerous device, or drug - just a machine that helps be to be able to breathe. The manufacturer could not ship the oxygen generator, which I desperately needed, until my pulmonary doctor sent him a prescription. Ironically, my pulmonary doctor was one of my students when I was technical director of the Cardio-Pulmonary Division of Johns Hopkins Hospital.
Now, I realize that some folks wish to have every safety item at their disposal aboard their boat, especially while cruising. And, I agree to a major extent. I carry a military (US Army) first aid field kit, which mainly consists of adhesive bandages, tapes, a suture kit, various antibiotic salves, sterile gauze, rubber gloves, eye wash system, aspirin, scissors, and a box of various sized Band-Aids. I also have a blood pressure machine (electronic), a stethoscope and a pulse oximeter, which tells me when it's time to go onto supplemental oxygen. I also carry my oxygen generator, which stays in the cabin, but I have a line long enough to reach my anywhere on the boat. It will run on the house batteries for about 72 hours. My second kit contains all my prescription drugs that I take on a daily basis, and they are in the prescription bottles, which is mandated by federal law. These include: Nitroglycerine (just in case), Albuterol (rescue inhaler), Metatoprolol (beta Blocker), Hydro-Morphine, Hydrochlorathiazide, an over the counter antihistamine, Zantac 150, 5,000 USP Vitamin D and regular aspirin. I also have a good supply of sunblock onboard, which every boater should have available for themselves and the crew.
Now, I do not, by any means, have all the bases covered if I encounter many medical problems while cruising. And, despite working the medical field for 15 years at two of Maryland's most prestigious hospitals with some of the top physicians and surgeons in the region, and extensive training at NIH and both hospitals, without having the proper diagnostic equipment at my disposal, and consulting with various specialist in the field, would not want to treat myself or others for anything other than minor cuts and scrapes. From what I've seen in that kit, it does not really address this without first having a rudimentary first aid kit onboard.
Good luck upon whatever you decide,