Sad to say, there are still many on this God-forsaken planet who think that there are demons just waiting to possess people. The case of Sangeeta Persaud comes to mind.
This poor child died as a result of an exorcism. Simple treatment of convulsions would have left her much better off. Stupidity reigns I am afraid.
Now that's not to say that demons do not exist. Nor that they cannot have influence over people. But such cases are extremely rare and the treatment in such cases does not involve the excessive consumption of lime juice, nor pounding on the stomach.
Mental and emotional sickness account for many alleged cases of demonic possession. And possibly possession may account for a few cases of madness.
Before you rush off to have some untrained amateur attempt an exorcism of you or someone in your family who is relying on you for their well-being you should do a little common sense research. This involves getting medical opinions as well as spiritual ones. It also involves consulting professionals in the field (paranormal or otherwise) which very often does not include those who are locked into religious dogma.
Get professional help. If you want to seek the assistance of someone in the paranormal field, then that's fine. But find out about their experience, their qualifications - and what they intend to do. If it involves bondage, violence or any other such stupid (and in terms of demonic possession, useless) practices, then move on to someone else.