TweetI've used it subcutaneous at 400mg/day. I noticed a difference in only a week. However, I had to stop use as after the first week I started having EXCRUTIATING pains in my head any time I physically exerted myself, whether it be running or lifting. I couldn't workout for almost a week. I just started running L-Carnitine again, this time IM. I think that it will be released more slowly and steadily if injected twice a week IM (the package insert recommends this). I'll let you know how things are going in a week or two.