I would at least use a 1.5in needle to get good and deep into the muscle. When injecting take your time. Plunge the sust in slowly to avoid irritating the muscle. Then after injection massage the area for 3-5 minutes. Also, do your injections in the morning so that you work the muscle throughout the day. If you can, work the muscle that you inject into on the same day that you inject. Never inject right before bed either when trying to minimize irritation. That's what I have found to be helpful in minimizing pain associated with certain injectables,,,bigjosh