study for long term enema used was already done by Dr Hiromi Shinya. He found that coffee enema will only improve the intestinal motility or intestinal phase rather than slowing it down based on his more than 30000 endoscopy and colonoscopy examination. A lot of health issue can be solved by washing your colon and changing your diet. Some of his patients had even abused laxative for their whole lives but then cured by three months of daily coffee enema, that means no need for laxative to have a normal bowel movement. The doctor has also used coffee enema for more than 30 years for himself and no ill effect had been found.
So conclusion is that enema will only improve the motility rather than make you depend on it like laxative. The body cleansed feeling could impact you on doing more enema rather than laxative like addition.
The reason why laxative is additive and bad is because it changes the color of the bowel and you can see it through colonoscopy.