At first I thought you were talking about MCT oil while on keto (adding it to coffee, etc)..... I've only used one product from a now defunct lab (Test E) and after the shot for three days it was painful/inflamed but the pain subsided after those three days, I took another shot it still hurt but it seemed to disappear after three days again. I kept on taking shots and each time it was less and less. All that I can tell you is for me it seemed like my body just wasn't used to it at first and maybe "adapted" to it each time less and less pain. That was my only experience with it, but I plan to make my own version for myself with a hopefully a high quality MCT oil hopefully I don't have to go through this all over again so I'm still a bit wary.