It's also often the butt of many, many a joke. (Forgive me for that one. I couldn't help myself).
In modern medicine enemas are most frequently used to help with constipation, clear the bowel out prior to a surgical procedure such as a colonoscopy or to help in imaging, for example in a barium enema.
However it may surprise you to know that history of human's sticking fluid up their rectums is a long and, well, somewhat obsessed one.
The first documented use of enema's goes back to the Ancient Egyptians. Reports of enemas have been found for many uses, from treating haemorrhoids to being part of the embalming process. The pharaoh's had a physician on staff who made enemas, and the God Thoth was said to have invented the procedure (amusingly enough he was originally the moon god).
The Greeks too mentioned enemas in their medical texts. The word 'enema' itself derives from Greek. In the second century Celsus suggested an enema as a way of introducing nutrients into the body during dysentery (infusing pearl barley - which frankly sounds horrible to me, but ok then). Galen the Roman 'father' of modern medicine also made frequent mention enemas of oil, water and honey to treat everything from fever to the 'female flux'.
References can also be found to enemas in Babylon and Assyria as early as 600 BC, Hindu texts, Nigeria and the inhabitants of the Ivory Coast.
You name the place - you can probably eventually find a fairly early reference to an enema.
(enema device made from animal gut - from eskimo culture - source - Wellcome images)
From the 1400s syringe enemas were increasingly invented and used (prior to that most images show something akin to a pigs bladder with a tube attached). In the 1600s a self administering enema syringe was invented so that enemas could be administered at home. From the 1860s onwards this would often come equipped with a vaginal tube so that contraceptive douches could also be given on the same machine.
(A pewter self- adminstering enema apparatus circa 1822-1846 - source Wellcome images)
Enemas were even used for resuscitation. In London in the 18th century, with the idea of saving drowning people and sponsored by the Queen herself, the Royal Humane society somehow hit on the idea of tobacco enemas. The idea being to warm the drowned person and stimulate their breathing. If this didn't work artificial respiration was commenced. To this end tobacco enema kits were placed at intervals all along the Thames.
Unsurprisingly no one was saved - but tobacco enemas briefly became very popular all across Europe for just about every ailment you can think of until it was discover in 1811 that nicotine is actually a fairly toxic substance. Now, of course, you all know the origin of the term 'blowing smoke up your arse'.
(tobacco enema kit - source Wellcome images)
Enemas fell out of fashion in the 19th and early 20th century with the advent of better oral laxative medication. Equipment continued to evolve with the brief advent of colonic hydrotherapy. The late 20th century has seen the invention of the so-called 'microenema' - the smaller, more efficient enemas which are largely in use in hospitals today.
However - enemas continue to be widely used in alternative medicine circles with colonic irrigation still very popular despite limited health benefits and the rise of the coffee enema. Despite the claims of its proponents - coffee as an enema substance was first used in 1917. Various claims have been made about how coffee enemas can do everything from detoxifying the liver to curing cancer, the reality in the literature seems to be more along the lines of burns, rectal perforation, electrolyte imbalances, dehydration and a few deaths have been reported.
The moral of the story being that if you wish to indulge this particular human habit - it might be best to choose a microlax!