There is no doubt that running can and will become an addiction if you continue to do it. Any addiction can be bad for you. A running addiction can cause you to run when your body needs rest, and you can injure yourself badly. A running addiction can cost you many hours of time that could and should be spent doing other important things. Now, I'm fixing to promote the whole "running addiction thing," but first I just wanted to clarify that yes, it can be bad if it is not kept in check!
Having got that warning out of the way, let me point out that there are good addictions and bad addictions. Typically this is how you can tell the difference: bad addictions are easy to pick up and hard to quit, and good addictions are hard to pick up and easy to quit. You won't get addicted to running by forcing yourself to do it a couple days a week for a week or two. You will have to force yourself to endure the pain and the soreness, and to keep getting out there to run even when you don't feel like it, until one day you realize that you can't wait to go for your next run. This is how good habits are acquired. The bad ones come very easily!
So what is so good about a running addiction? Well, there are obvious benefits one can gain from running. Most noticed benefits are probably weight loss (realize that changes in diet will most likely be necessary as well) and an increase of endurance and energy during one's daily activities. Usually, there is an all-around sense of "feeling good" that can't really be explained, but here are a few reasons you might start feeling better:
-Stress relief -Increased blood flow and oxygen levels -Vitamin D (if you are running outside) from the sun -A sense of achievement and self-confidence -A willingness to become disciplined in other areas of life -More energy to do things that are very satisfying (playing with the kids, getting projects done that you've been putting off) -Allergy symptoms are often reduced -Body's Immune system is usually strengthened (providing you are also getting rest) -Less likely to suffer from a cold or flu...
I'm sure I'll be adding to this list later, but these were the first benefits that came to mind. You can see there are great benefits to becoming a running addict. If you are beginning a running program, training for a race, or just want to get into shape, I hope you will stick with it until it becomes a habit. But, as with all habits, run responsibly!