There's a scientific name for it: onionmania. It means that you can't quit shopping, even when you don't want or need anything. You get a "high" from buying things, then you fall to a painful low when you bring them home and realize what you've done. Tammy Ruggles wrote a piece for Dollar Stretcher called "Are You a Shopaholic?" in which she lists symptoms of this disease... or disorder. Or whatever you call it. No one seems to know just how to categorize it.
If you think you have this or know someone who does, the "quick fixes" she lists do more than just take care of it for today. Limiting shopping excesses can be done by taking a limited amount of cash - no checks or credit or debit cards and it can be done by taking a friend or spouse who will keep you accountable. Sticking to a list works for some, but it's not the easiest way to tackle the problem.
When the urge to shop strikes, try getting your "fix" for free or cheap. Go to the library and borrow books, CDs, DVDs, paintings... whatever they have that you like. Go garage saling or thrift store shopping rather than retail shopping but still carry a limited amount of cash.
We all have the urge to get something new now and then just because it's there and there's nothing wrong with that as long as we can afford it. When it becomes more than a "now and then" thing and we really can't afford it, it can cause a sound financial ship to sink. Get help if you need it. Counselling is available, and although credit counseling can be free, it may not do the trick. Go to a psychologist if you can. Even if it's expensive, you may very well save money in the long run.