I've heard they are using laughing gas to treat tennis elbow. How does that work?

You may be confusing nitrous oxide with nitric oxide. Nitrous oxide is what we also know as laughing gas used to relax dental patients. Nitric oxide is a cellular molecule that appears to have a wide variety of functions. For example, it acts like Teflon in the blood vessels to keep blood moving smoothly. It also enhances tendon healing. By improving blood flow, it helps improve memory and blood pressure.

Treatment is with patches placed over the painful area. Nitric oxide in the patch is absorbed by the area of tendon damage promoting healing. Studies using the patches for six months showed improved function and strength because of decreased pain. And the pain relief can occur as fast as 24 hours after starting the patch. Nitric oxide provides more than just pain relief. There's evidence of actual tendon healing as well.

Studies in animals and humans using nitric oxide for tendonitis and tendinopathy are ongoing right now. With tendonitis, there is acute inflammation. Tendinopathy refers to a condition with tendon degeneration but no active inflammation. These studies may help us better understand the mechanism by which nitric oxide works for these conditions.