Did medieval kingdoms issue health related guidelines?

We've had some Covid 'guidance' that was mandatory, so I'll merge guidance/rules in this answer.

A useful trick was to make the 'guidance' a religious matter. Sidesteps all that personal judgment question about whether guidance should be followed or not. As the bible says, pork, camel and rock-badger are unclean meats.

It was a little after the medieval period (though very British), but King James' A Counterblaste to Tobacco from 1604 is an oft-cited early example of public health guidance and one of the earliest texts to specifically identify specific health risks of smoking (emphasis mine below). It also identifies smoking as a poor social skill and alludes to its addictive nature. It also (very interestingly!) compares some possible medicinal value of tobacco with "abuse", foreshadowing the modern distinction between drug "use" and drug "abuse".

Have you not reason then to bee ashamed, and to forbeare this filthie noveltie, so basely grounded, so foolishly received and so grossely mistaken in the right use thereof? In your abuse thereof sinning against God, harming your selves both in persons and goods, and raking also thereby the markes and notes of vanitie upon you: by the custome thereof making your selves to be wondered at by all forraine civil Nations, and by all strangers that come among you, to be scorned and contemned. A custome lothsome to the eye, hatefull to the Nose, harmefull to the braine, dangerous to the Lungs, and in the blacke stinking fume thereof, neerest resembling the horrible Stigian smoke of the pit that is bottomelesse.

My "modernization" of the above (not really a translation since it was already in Modern English, but rephrased in a more 21st century manner):

You should be ashamed of yourselves and quit this filthy habit that you were foolish and stupid to get into. By abusing tobacco, you sin against God and harm both your health and your finances. You also look vain and foreigners stare at, scorn, and condemn you when they see you smoking. Smoking is bad for the eyes, nose, brain, and lungs, and looks like the smoke that rises from Hell.

While this document lacks the medical precision of more recent guidelines, it is a clear example of public health guidance of yesteryear - a document issued by a king, not as regulation, but as guidance to encourage healthy behavior in his subjects.

Also do read its 17th century depiction of drug addiction, still quite easy to understand today and also substantial documentary evidence that drug addiction was well-known hundreds of years ago:

And from this weaknesse it proceeds, that many in this kingdome have had such a continuall use of taking this uusavorie smoke, as now they are not able to forbeare the same, no more then an olde drunkard can abide to be long sober, without falling into an uncurable weaknesse and evill constitution: for their continuall custome hath made to them, habitum, alteram naturam: so to those that from their birth have bene continually nourished upon poison and things venemous, wholesome meates are onely poisonable.

My "modernization" of the above:

This weakness is evident in the fact that so many people in this kingdom have been smoking this unsavory substance for so long that they can't quit without getting sick, just like alcoholics can't quit drinking. Their constant smoking has turned their habit into their nature, just like those that have grown up consuming poison and venom find that healthy food is poisonous to them.

One famous source for life during medieval pandemic is the introduction of Boccaccio's Decamerone, which describes the Black Death in Florence in 1348:

And against this pestilence no human wisdom or foresight was of any avail; quantities of filth were removed from the city by officials charged with the task; the entry of any sick person into the city was prohibited; and many directives were issued concerning the maintenance of good health.

(emphasis mine)

If you count quarantine measures (in the sense that travellers cannot enter a port or city before waiting a number of days without getting sick), those were also imposed by local authorities. The word "quarantine" itself stems from the 15th century, but a "trentine" (30 days) was already practiced in the 14th century.