Can only the possessed person cause that ''spirit'' to stay or can someone else give it power to stay??
Greetings, dear WS, and the greatest of love and peace to you! If the possessed person does not desire the spirit to stay, he/she can remove it, themselves; however, if they are weak... or do not fully realize the possession... so that another's "will" is stronger than theirs, that other can give it power to remain. The possessed person doesn't HAVE to be stronger or fully realize the possession, though. Another... or others... whose [combined] will IS stronger than the one who desires the spirit to remain... can conquer and cast it out. Depending on how weak the possessed person is... and how strong the will for the one wishing the spirit to remain is... it might take more than one to overcome it... sometimes even with fasting and prayer. It depends.
BUT... it is not a thing to be afraid of. It is not like in the movies where heads spin and backs bend... and green vomit is projected across the room. No floating in the air or opening/slamming doors/drawers and the like. The manifestation is with the person who is possessed. True, they may have certain "fits" and [appear to] throw themselves down, but that is because they are the ones being harmed. The reasoning of the spirit is that if it can cause enough fear people will back off. Even the possessed one will concede and allow it to remain just so the greater "trauma" (it seems) will cease.
Can medication help? Again, yes. It can sedate the BODY as well as the mind, so that the spirit cannot have its will done. However, the medication won't release the spirit. It is still there and as soon as the medicine wears off will commence its antics again. Which is why such folks have to stay on medication perpetually.
[Now, I understand that some will believe that that is "best" because they believe these things to be purely biological (and in some instances perhaps they are). Perhaps. If that is the case, however, it would seem that something... medication, surgery, something... would cure it. However, these are instances where, for all intents and purposes, "medicine" has NOT worked. Personally, I think that doing away with the CAUSE of the "illness", rather than just dealing with the SYMPTOMS is "best"... for the person. But doing what's "best" for "society" often outshadows what's "best" for an individual (surely, we can't have these people walking around without medication, although they do appear to be cured - what if they have a relapse and hurt someone? Oh, wait, they never hurt anyone else - only themselves, but still...)].
But I'm just a servant and not a "medical expert", so...
But, yes, dear one, someone else can give it power to stay. I would say to anyone who has this dilemma... don't ALLOW them to give it such power. If you are weak... ASK FOR HELP. It WILL be given you. Either directly or through others. And no, it is not through "hocus pocus" or medieval rituals such as exorcism or bloodletting - . The only "extreme" things that might be involved is prayer... and fasting (3-7 days). The fasting MUST be voluntary, however, as to the possessed person (although, they don't necessarily need to fast, indeed, they might not be able to); no one should ever arbitrarily withhold food from another person, for ANY reason. Won't work in such a case, anyway.
I hope that helps, dear WS. Folks don't always realize that it is we who allow place for such things... either on our own behalf (through excessive alcohol, drugs, fear, etc.)... or on behalf of others (by putting fear in THEM; for example, in our children...).
Peace to you!
Your servant and a slave of Christ,