Why do I still have pain today after the intramuscular injection in my buttocks yesterday? It is because the injected drugs after intramuscular injection will cause local inflammatory reaction, and at the same time, because the capillary bleeding caused by the puncture needle will also cause local inflammatory reaction, both of which will cause local nerve stimulation and cause pain. Therefore, sometimes the pain may even last for 2-3 days before absorption. If there is no localized subcutaneous bruising and swelling, redness, elevated temperature, etc., the pain can be gradually recovered, which is also a normal phenomenon, and there is no need to be nervous. If the pain is heavier or the surrounding obvious redness, this situation needs to go to the hospital.