Sadly, Christians can certainly be troubled and possessed by demons. If a person becomes disobedient to God and strays into the occult, spiritism, shamanistic worship, hypnotism, drugs, idol worship, traditional religion (Voodoo) etc., that poor person is in serious danger.
Those who were afflicted by demons in Jesus’ day:
Matthew 8:16, “When the even was come, they brought unto him many that were possessed with devils: and he (Jesus) cast out the spirits with his word…”
Jesus freed many who were demon-possessed and had specific authority over evil spirits.
While we do believe fallen angels are quite active, it may be difficult today to discern if there is actual demon possession vs. mental illness or brain damage from a proliferation of drug use. Appropriate medical treatment should be sought first.
Exorcism is not simply the recitation of a formal command. Only a truly consecrated, mature Christian might even consider such an action. Remember the account in Acts 19:13-17:
Some Jews who went around driving out evil spirits tried to invoke the name of the Lord Jesus over those who were demon-possessed. They would say, ‘In the name of the Jesus whom Paul preaches, I command you to come out.’ Seven sons of Sceva, a Jewish chief priest, were doing this. One day the evil spirit answered them, ‘Jesus I know, and Paul I know about, but who are you?’ Then the man who had the evil spirit jumped on them and overpowered them all. He gave them such a beating that they ran out of the house naked and bleeding. When this became known to the Jews and Greeks living in Ephesus, they were all seized with fear, and the name of the Lord Jesus was held in high honor.
This story teaches that the name of the Lord Jesus had to be used to cast out a demon. But the speaker had to have a close walk with God and be in the correct heart attitude.
However, it is important to remember that there is no New Testament instruction to believers how to cast out a demon or direction that we are supposed to do so. Better to follow the admonition to put on the whole armor of God (Ephesians 6:10-18) and stand firm in the light.
A person who feels demon-influenced might ask a mature Christian to stay with or accompany him or her for several days. Whenever the troubled one might feel bothered by demons, the Christian could calmly reassure that one with Bible verses and prayers that God is with them.
Remember the promise, “Therefore submit to God. Resist the devil and he will flee from you. 8 Draw near to God and He will draw near to you. Cleanse your hands, you sinners; and purify your hearts, you double-minded.” James 4:7-8.
To learn more about demons today listen to, “How Do Demons Influence Our World?”