Hyaluronic acid is not a drug but is a natural chemical that is found within the body. It is present in a particularly high amount in joint tissues and in the fluid that fills the joint (also called synovial fluid). Hyaluronic knee injections work differently than oral pain medications. Knee injections do not pass through the bloodstream to work. Hyaluronic acid knee injections are injected directly into the knee, so it does not cause stomach bleeding problems like some pain medications. Hyaluronic acid knee injections can provide long-lasting pain relief for up to 6 months and can be safely used for up to 30 months.