The idea that it was an addiction was once presented to me by someone who seemed to think that just recognizing that it was like an addiction would be enough to stop it.

It's not that easy, is it? I think that first of all you need to find something to replace it with (I know you go running - sometimes that might be the right thing. When you can't go running, what else might you try? talking to someone? something from the list that was posted here a few days ago?) I know that when I try to stop I just find something else to do instead - not eating, not drinking water, getting a bad sunburn, ...) So, find something constructive to replace it with.

Actually have a plan and write down on an index card what you will do when you want to hurt yourself so that you can pull it out and look at it when you need to.
You could set up a chart or just put a smilie face on the date in your calendar or something to reward yourself for not doing it. After a certain number of days, give yourself a tangible reward - something of your choice. Start with just a few days at first, and gradually increase the time to earn the reward (the reward can get bigger for longer time periods too).
Then, there is also a medication that blocks the effects of the endorphins. I posted that before, but if IIRC it is called Rexia. Ask your doctor about it.
I guess you could try going to a 12-step program for help. They have those for all kinds of addictions and also for depression and stuff too.
In my opinion, I feel that tapering off would be better than cold turkey, unless you find that once you have hurt yourself it increases your desire to do it again. Then you would need to try cold turkey.
Good luck!
-Wendy
<font color=purple>"You may be disappointed if you fail, but you are doomed if you don't try."</font color=purple>
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“We should always pray for help, but we should always listen for inspiration and impression to proceed in ways different from those we may have thought of.”
– John H. Groberg