It depends. The majority of stones are calcium based and once they form they are almost impossible to dissolve. 6 cm is a very large stone and usually this would be treated percutaneously (through a 1 cm opening in your back going into your kidney). We place a small sheath and break the stone into tiny pieces and pull them out through the sheath. A patient stays overnight in the hospital and usually leaves the next day without any tubes or drains.
There are about 15% of stones that are made of uric acid. These can be dissolved by raising the pH of the urine. I usually do this with potassium citrate. It would take a long time to dissolve a 6 cm stone. One option would be to break it up with lithotripsy (ESWL) to give it more surface area. If you did that you would need a stent so the pieces don’t plug up the ureter. I hope this helped.
A note added in 2026. This post gets found by a lot of people who typed "6 cm" but whose report actually says 6 mm, or 0.6 cm, which is a completely different situation and a far better one. If that is you, read Kidney Stone Size: What Passes on Its Own and What Doesn't instead.