What are the halakhic guidelines and limitations for using psukim from the Torah to heal illness? Does it make a difference if the psuk is being used to heal a "spiritual" malady which is believed to be causing the physical one? What if the psuk is being used as part of tikkun to rectify a sin which is causing the ailment?
Shulchan Aruch, Yoreh De'ah 179:5 (citing Sanhedrin 90a and 101a), states:
Shach (ibid. :10) says that this primarily refers to using a verse containing G-d's name, because it is grossly disrespectful to associate that with spitting. So using a verse that doesn't contain any Divine name may just be forbidden (without incurring the penalty of losing his share in the World to Come).
Taz (ibid. :7) concurs. He goes on to say (ibid. :8) that the general rule is that "words of Torah were not given for the healing of the body, but for that of the soul," and that this is why this practice is prohibited, unless the person's life is in danger.
Finally, Shulchan Aruch (ibid. :10) says that all of this applies only when the person is already injured or ill, but that "a healthy person may recite verses to protect himself from destructive forces" - which, as Taz (ibid. :8) points out, is indeed the reason we recite the bedtime Shema.
The Rambam in Hilchot Avoda Zorah, Chapter 11, Law 13 (or 12 depending on edition) states:
יג [יב] הלוחש על המכה וקורא פסוק מן התורה, וכן הקורא על התינוק שלא ייבעת, המניח ספר תורה או תפילין על הקטן בשביל שיישן--לא דיי להן שהן בכלל חוברים ומנחשים: אלא שהן בכלל הכופרים בתורה, שהן עושין דברי תורה רפאות גוף, ואינן אלא רפאות נפשות, שנאמר "ויהיו חיים, לנפשך" (משלי ג,כב). אבל הבריא שקרא פסוקין או מזמור מתילים, כדי שתגן עליו זכות קריאתן, ויינצל מצרות ונזקים--הרי זה מותר.
"A person who says an incantation over a wound and recites a verse from the Torah, who recites a verse over a child so that he will not become scared, or who places a Torah scroll or tefillin over a baby so that it will sleep, not only is considered to be a soothsayer or one who cast spells. Furthermore, such people are included among those who deny the Torah, because they relate to the words of Torah as if they are cures for the body, when, in fact, they are cures for the soul, as [Proverbs 3:22] states: "And they shall be life for your soul. It is, however, permitted for a healthy person to read verses [from the Bible] or chapters from Psalms so that the merit of reading them will protect him and save him from difficulties and damage."
It would seem according to the Rambam, that to recite Pasukim (verses) to heal a person would be prohibited at all times. I would assume a כופר בתורה, would have no portion in the world to come as well.
It would further seem that to say Tehilim for a sick person would be problematic as well. Unless the person is learning the Tehilim to raise their level, and then engages in prayer. This is probably why we are accustomed to saying a Mishaberach after saying Tehilim on behalf of a sick person. In other words, the Tehilim function as a precursor or preparation for the person engaging in Prayer. Much like we do for Mincha by saying Ashrei before the Shmoneh Esreh.
The discussion really is about saying Tehilim for the sick. Rav Asher Weiss (a Posek) rules that it is Mutar because "Minhag Mevatel Halacha." Rav Meir Eliyahu also discusses the prohibion of Tammim Tihye in regards to going to fake "mekubalim" for them to check your hand (Orhot Sadikim Shaar Yirat Shamayim at least 800 years ago as Rambam quotes him says we lost this practice as brought down in Zohar 1:170), and he also rules that this Asur Mideorayta as brought down in Wayashob Yam 2:12-13.