Generally speaking, it's trickier to tailor leather than most other fabrics. That said, it is entirely possible to alter leather and suede if you go to the appropriate professional. If the coat is of great sentimental or financial value, I would only take it to a tailor who has been recommended to me personally; I would ask to see other work first, and discuss precisely what work would be done. To find your nearest tailor, use www.upmystreet.com.

If, however, it's a complicated cut (a biker jacket, for example), you'd be way better off selling it and starting over. Look upon it as your treat for losing weight!