Clyster is an old-fashioned word for enema, more particularly for enemas administered using as clyster syringe — that is, a syringe with a rectal nozzle and a plunger. Clyster syringes were used from the modern era to the 19th century, when they were largely replaced by enema bulb syringes, bocks and bags.

The patient was placed in an appropriate position (kneeling, with the buttocks raised, or lying on the side); some servant or apothecary would then insert the nozzle into the anus and depress the plunger, resulting in the liquid remedy (generally, water, but also some preparations) being injected into the colon.

Because of the embarrassing aspect, for a woman, of showing one's buttocks (and possibly one's sex, depending on the position) to a (male) apothecary, some contraptions were invented that hid the whole behind except for the anal area. Another invention was syringes equipped with a special bent nozzle, which enabled self-administration, thereby eliminating the embarrassment.

Clysters were administered for symptoms of constipation - and with more questionable effectiveness; stomach aches, and other illnesses.

The clyster craze of the 17th and 18th centuries

Clysters were a very favorite medical treatment in the bourgeoisie and nobility of the Western world up to the 19th century. As medical knowledge was fairly limited in those days, purgative clysters were used for a wide variety of ailments, the foremost of which were stomach aches and constipation.

Molière, in several of his plays, introduces characters of incompetent physicians and apothecaries fond of prescribing this remedy, also discussed by Argan, the hypochondriac patient of Le Malade Imaginaire . More generally, clysters were a theme in the burlesque comedies of that time.

In the 18th century, Coffee clysters were taken by some people who wanted the effects of caffeine but disliked the taste of coffee. Tobacco smoke clysters were administered to fainting women, hence the term "to blow smoke up her ass".

According to Saint-Simon, clysters were so popular at the court of King Louis XIV of France that the duchess of Burgundy had her servant give her a clyster in front of the King (her modesty being preserved by an adequate posture) before going to the comedy.