obstacles to healing

God operates on the basis of His promises and His glory.  We must learn how to negotiate with God through these things.
Here's a examples of Moses, Nehemiah and Daniel doing just that:  http://orderofsaintpatrick.org/salt/intercession.htm

Here are some things that inhibit God healing someone:

1. You have not because you ask not.  
2. You pray simply for your own selfish pleasure (idolatry of self).
3. You didn't ask God for the Gift of Healing of whatever they have.
4. You are involved in occult practices.
5. You are a member of a group you identify with that practices or has practiced the occult.
6. You may have idols or charmed objects in your environment.
7. Witches or a shaman are sending demons to you.
8. You may not have that specific gift of healing.
9. It may be augmented or caused by poisons, medicine side-effects, DNA damage, T cells attacking the body, chronic stress, poor eating and hormone imbalance.

All of this is why we need to pray for gifts of the Holy Spirit so God can tell you or show you what it is you are dealing with.  Or you can ask God to use you and let Him speak through you for the person.  Amazing things can come out of your mouth that you have never heard before.