Corticosteroid injections can take varying amounts of time to reach their maximum effectiveness, depending on the specific type of corticosteroid used. It is generally advised to avoid corticosteroid injections in cases of kidney insufficiency. Corticosteroids taken by mouth, such as prednisone, can have different effects on blood pressure and blood sugar compared to corticosteroid injections. It is always best to consult with a healthcare provider to determine the safest and most effective treatment option for your specific condition.