How long will the pain relief last? It usually starts to work within 24 to 48 hours. Pin On Health - The True About Food Drugs Talk to your physician about it. How long does a cortisone shot take to work for sciatica . In most cases, the shots only last about 3 months. It did help with my sciatica. If the dosage is reduced too quickly, your adrenal glands may not have time to recover and you may experience fatigue, body aches and lightheadedness. It will be several days before the steroid medicine starts to work. There are some side effects associated with cortisone shots. Maybe a few hours of slight relief. Taken together, the four studies show that patients who got epidural steroid shots had a slight drop in pain two to six weeks after the injection, compared with patients who got epidural shots. But relief doesn't last very long. To give your adrenal glands time to recover this function, your doctor may reduce your dosage gradually. In some cases, ...