Hey Silver,
I'm a writer too, and there are a few issues with self-publishing. It really depends on what you want from writing and any future publishing hopes.
If you self publish a book (we're not talking just binding up your work to look like a book, I mean isbn number and all that stuff) then there is a very large chance you'll be blacklisted from the big publishers. It's quite terrible, this, because it's so difficult to get published, but my old writing teachers taught us that thats normally the way it goes. They want you go to through things the "normal" way, that is, with them in charge. That being said, self-publishing and big amounts of promoting CAN work out for you (think Eragon, that 15 year old kid's book, way back when, that he published himself and them promoted like crazy with his family) but that only works if you make a ton of money and then a publisher wants to pick you up.
So, I haven't gotten my book published either, but i'm not going to self publish, because i'm hoping that writing will be something I do for the rest of my life, something I want to do and get published. I don't want to risk it.
HOWEVER and this is a big however. if you are not looking for a career in writing along with your medical career (not everybody needs to be oliver sacks, or can be) then I wouldn't worry too too much. Its not a guarantee that you'll have a hard time later publishing, especially if you have a pen name or a different genre (i'm not too sure about how that affects you) but there is that chance.
The other question is patience. I don't know how much or how long you've written (you should tell me in another post! i'm curious, congrats on completeing a book, btw) or what genre you write it, but it can take years to get a book published. A prof. of mine, already a noted author, waited three years for her book (fantastic book) to be picked up and published. there is an unfortunate amount of waiting involved.
Interestingly enough, often times when you see a popular "first" book published by an author and then 3 months later out comes the next book, it's not because they wrote a quick book, but because that second book was usually the first one they wrote. tonnnnsss of waiting
If your primary concern is being able to tell adcoms you've had a book published, then by all means publish it knowing the risks and what you want out of your writing.
If you've written a book, and you have, there's no risk in letting people know you've written a book. On my AMCAS application I talked about writing my book. While I did win a small something local for the book, i haven't gotten it published and have no leads for getting it published in the immediate future. But i did it, and i mentioned it, because it took a long time and it was a lot of hard work, and heck, its quite the extracurricular achievement. Congratulations. So, tell me, what is your book about, what kind of writing do you do, is this a first career? or are you a college student, etc 🙂 Nice to be running into a few authors here on SDN. We should start trading fiction 🙂 I love the med schools that have the lit and art journals that their students contribute to!!!