Synject Injection is used in the treatment of pain in osteoarthritis of the knee in patients who have failed to respond adequately to non-pharmacologic therapy, nonsteroidal anti-inflammatory drugs (NSAIDs), or simple analgesics (pain killers). It contains Hyaluronic acid, which works by reducing friction between the joints. Thereby providing relief from pain. In some cases, it may cause common side effects such as diarrhea, headache, loss of appetite, nausea, vomiting, and stomach pain. Before taking this medicine, you should tell your doctor if you are allergic to any of its components or if you are pregnant/breastfeeding.