Humorism, or the notion that human health depends on a balance of fluids (or "humors") in the body, was a predominant paradigm in health from the time of Hippocrates until the general acceptance of the germ theory of disease. It was believed that there were four humors: blood, phlegm, yellow bile, and black bile. Disease and mental illness arose from an imbalance in one's humors, and treatments ranged from the prescriptions of certain foods and drinks to increase one humor or decrease others, to bloodletting and other direct manipulations of the humors.

An 11th century poem attributed to John of Milano describes the symptoms of an overabundance of each of the humors (this is just an excerpt):

If Sanguin humour do too much abound,

These signes will be thereof appearing cheefe,

The face will swell, the cheeks grow red and round,

With staring eies, the pulse beate soft and breefe,

The veynes exceed, the belly will be bound,

The temples, and the forehead full of griefe,

Unquiet sleeps, that so strange dreames will make

To cause one blush to tell when he doth wake:

Besides the moysture of the mouth and spittle,

Will taste too sweet, and seeme the throat to tickle.

If Choller do exceed, as may sometime,

Your eares will ring, and make you to be wakefull,

Your tongue will seeme all rough, and oftentimes

Cause vomits, unaccustomed and hatefull,

Great thirst, your excrements are full of slime,

The stomacke squeamish, sustenance ungratefull,

Your appetite will seeme in nought delighting,

Your heart still greeued with continuall byting,

The pulse beate hard and swift, all hot, extreame,

Your spittle soure, of fire-worke oft you dreame.

If Flegme abundance haue due limits past,

These signes are here set downe will plainly shew,

The mouth will seeme to you quite out of taste,

And apt with moisture still to overflow,

Your sides will seeme all sore downe to the waist,

Your meat wax loathsome, your digestion slow,

Your head and stomacke both in so ill taking,

One seeming euer griping tother aking:

With empty veynes, the pulse beat slow and soft,

In sleepe, of seas and ryuers dreaming oft.

But if that dangerous humour ouer-raigne,

Of Melancholy, sometime making mad,

These tokens then will be appearing plaine,

The pulse beat hard, the colour darke and bad:

The water thin, a weake fantasticke braine,

False-grounded ioy, or else perpetuall sad,

Affrighted oftentimes with dreames like visions,

Presenting to the thought ill apparitions,

Of bitter belches from the stomacke comming,

His eare (the left especiall) euer humming.

Mood/personality descriptors based on the four humors are still in usage, though infrequently and largely divorced from the idea that one's fluids might actually be out of balance. If you've heard of someone being described as "phlegmatic," "sanguine," "choleric," or "melancholic," those terms arise from the four humors. In fact, the word "humor" itself as a modern synonym for "comedy" comes out of Renaissance comic plays -- specifically those of Ben Johnson -- in which characters represented exaggerated imbalances of the humors for comic effect.

I'm surprised this has not been mentioned yet, but eugenics was very popular in the Western world and was practiced all the way up until the 1970's, and was very popular among people all across the scientific world and the political spectrum. However, eventually scientific advances as well as moral concerns ruled most of it out, as the genetic sources of abnormalities are far more complicated than Eugenicists thought, among other reasons.

According to John Quincy, in his book "Lexicon Physico-Medicum" (1767), doctors should refrain from the following practices...

• Hanging a sign that says ABRACADABRA around the patients neck. Although this has been assigned curative powers by Serenus in his work "Medicina Metrica", Quincy condemns this as a trick and as laughable in modern medicine.

• Amulets as medicine are often "much abused", but Quincy firmly states that a knowledgeable doctors "will find no Reason to disbelieve the possible Efficacy of Amulets".

• Quincy states that Incantations when applied with Charms, although supported by Paracelsus and Helmont and other chemical enthusiasts, is delusional and should pursue a "better Way of Reasoning".

• Necromancy that is espoused by some "enthusiastic Physicians" is purely a Juggle (deception), according to Dr. Quincy.

A lot of things being condemned by Quincy in this mid 18th century medical book are what we would call sympathetic magic today, but I don't think they have that term back then. When Quincy gets really riled up, he calls them "Jugglers".

This is not a direct answer, but something to take into account: some successful and thoroughly empirical disciplines have fizzled out because they exhausted their subject matter. They're still taught to undergraduates, and they may be important as technologies, but fundamental discoveries are few are far between.

In my own field, language and literature, I'm thinking about classical rhetoric, analysis of rhyme and meter in poetry, Indo-European historical linguistics, philology and paleography, phonology and phonetics (except its relation with neurology and AI).

I wouldn't put history in this category. New finds and new theoretical perspectives seem to keep this discipline alive. What do historians think?

Psychoanalysis, as a medical discipline. In the 1950s, a majority of papers published in clinical psychology and psychiatry journals referenced psychoanalysis or its concepts. By the late 1970s, it was below 1%, and mostly negative.

Some therapies ("psychodynamic") claim to be evolved from psychoanalysis but they either don't have much if any supporting evidence for their efficacy, are far removed in practice from historical psychoanalysis, or simply aren't any better than any form of talk therapy.

That's not to say it's not practiced anymore, far from it unfortunately, but it's declining. The theory is pretty much dead to science, as the huge advances in neurosciences in the past few decades usually contradict the unique claims of psychoanalysis. When they do, it's either the vaguest, unspecific notions (such as the unconscious) or those that aren't even original.