The WTS has moderated its position in recent years but still tends to speak out of both sides of its mouth leaving itself wiggle room.
*** w03 5/1 p. 31 Questions From Readers ***
If a Christian hears voices, does that necessarily mean that he is under demon attack?
No. While demons have been reported to manifest themselves in that way, many individuals who hear voices or experience other inexplicable, disturbing sensations have learned upon investigation that they have a medical problem.
Even in the first century, it was apparently recognized that demon attacks and physical conditions sometimes produce similar effects. At Matthew 17:14-18, we read of a young boy who was healed by Jesus. Although the young boy had manifested severe epileptic symptoms, his suffering was actually caused by a demon. However, on an earlier occasion when crowds of suffering people were brought to Jesus for healing, these included some who were "demon-possessed and epileptic." (Matthew 4:24) Evidently, it was recognized that some epileptics were not demon possessed. Their problems were physical.
It is reported that some who suffer from schizophrenia, a disease often treatable with medication, hear voices or experience other symptoms that could appear to be something uncanny. Other physical conditions may also cause mental confusion that some could mistakenly think is caused by demons. Hence, while an individual who reports hearing voices or who has other disturbing sensations may not want to discount demon harassment, he should definitely be encouraged to consider investigating whether there is a physical explanation for what he is experiencing.
See "Taking the Mystery out of Mental Illness," in the September 8, 1986, Awake!, companion magazine of TheWatchtower.
*** w88 10/15 pp. 27-28 Mental Distress—When It Afflicts a Christian ***
Afflicted by the Demons?
Some victims of mental difficulties fear they are under demonic attack, claiming at times to hear "voices." True, the demons have been known to make sane individuals behave irrationally. (Mark 5:2-6, 15) There is no proof that the demons are involved in most cases of bizarre behavior, any more than that they are involved in all cases of speechlessness, blindness, and epilepsy. Yet, back in Bible times, the demons sometimes caused (or at least aggravated) these very ailments! (Matthew 9:32, 33; 12:22; 17:15-18) The Bible makes a clear distinction, though, between "those who were ill and those demon-possessed." (Mark 1:32-34; Matthew 4:24; Acts 5:16) Obviously, then, the vast majority of cases of blindness or epilepsy today are caused by physical—not demonic—factors. The same no doubt can be said of most cases of mental distress.
Still, it must be remembered that Satan and his demons are ‘waging war’ with God’s people and have been known to harass faithful Christians. (Revelation 12:17; Ephesians 6:12) The demons are fiendish, and it should not surprise us that they take sadistic delight in tormenting some mentally distressed souls—compounding their difficulties.
So if the elders have good reason to suspect that demonic influence is involved, there is no harm in their making some inquiry. Has the person, for example, received any suspicious items directly and deliberately from individuals who are involved in some form of demonism? Disposal of such objects may bring relief. (Acts 19:18-20) Since Christians are told to "oppose the Devil," the elders can also advise the afflicted one to reject any strange "voices" that could be of demonic origin. (James 4:7; Matthew 4:10) If a person feels under attack, he should pray fervently, calling upon Jehovah’s name out loud.—Ephesians 6:18; Proverbs 18:10.
Demonic involvement, however, appears to be the exception—not the rule. One sister relates: "I thought I was possessed by a demon until I sought medical help and was informed that I had a chemical imbalance. It gave me great relief to find out that it was an illness that was causing my actions and not some demon person that was inside of me!"
*** w83 7/1 p. 28 Does God Care About the Mentally Ill? ***
The Basic Cause
In the past it was commonly believed that almost all mental disorders had supernatural origins, and some think this is the Bible’s view of mental disorder or insanity. True, the Bible does tell of cases where persons were possessed by invisible wicked spirits, but this does not mean that it stamps all kinds of mental disorder as demonic possession.
It must be remembered, of course, that the Bible is not a medical book describing the cause for different maladies. Yet it does explain what is the common cause for all human diseases, mental and physical. It shows that we are victims of the imperfection resulting in death that was passed on to the human race by our sinful forefather Adam. As the apostle Paul explains: "Through one man sin entered into the world and death through sin, and thus death spread to all men because they had all sinned." (Romans 5:12) This means that every descendant of Adam is imperfect and thus somewhat deficient both mentally and physically. Therefore, mental aberrations are but extreme forms of an inherited weakness we all have.