B Vitamins and acne?

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A thread about B Vitamins I posted in earlier today got me thinking about my own problem with B-12. Has anyone here experienced severe acne in conjunction with taking any kind of B Vitamin supplement? I've never had a problem with acne in my life, and for about two months (ever since I've started taking B-12), I've developed painful cystic pimples all over my face. My best friend is currently taking a B complex and having the same exact issue. After doing some research online, I've found that many B vitamins can cause acne in some people.

If you've experienced this and stopped the B, how long has it taken to see an improvement in your skin?