Home Diabetes Glossary regular insulin regular insulin Wednesday,January 4, 2023 ByDiabetesCare.net by DiabetesCare.net | Jan 4, 2023 | 0 comments short-acting insulin. On average, regular insulin starts to lower blood glucose within 30 minutes after injection. It has its strongest effect 2 to 5 hours after injection but keeps working 5 to 8 hours after injection. Also called R insulin. Submit a Comment Cancel replyYou must be logged in to post a comment.