Here is the mantra for healing gallstones. This was given by His Holiness Chobgye Trichen Rinpoche. There are different mantras in different texts, also. This mantra is to be blown on water mixed with butter:
OM SVABHAVA SHUDDHA SARVA DHARMA SVABHAVA SHUDDHO HAM
While everything is empty you manifest as Hayagriva, red in color, with the right hand holding a lotus and the left hand in the threatening mudra (middle and ring finger bent and held down by the thumb, with the little and pointing fingers curved like a horn, stretched out but not completely). Above your head is a green horse head. You are adorned with a tiger skin skirt.
Recite the following mantra:
OM BHUR KUM MAHA PHAR KHANA NA GHUTSA GHUTSA BE MA NATSE BHITA KORDHANI BHO GHUNG LING UTSA MAHA KORTHA HUM HUM PHAT PHAT SVAHA
Recite a few malas and after each mala blow over the water.
If you are doing this to heal yourself, then each time that you drink the water recite a few malas first and then blow over the water and drink it. Recite five, four, three, two, or at least one mala. The more you can recite the better.
If you are doing this for someone else, then it is better to recite the mantra many more times (as you have to bless the water all at one time). The best is to recite 10 or 7 malas, but at least 6. Recite as many as you can.
It is important to generate strong faith that by reciting the mantra, with all the blessings of Guru Hayagriva, it has all the power to heal the sickness immediately, as well as all the delusions, negative karma, spirit harms, and sicknesses.
With much love and prayers...