I was offered a position with several contingencies (drug test, background check and management interviews). It's been more than 4 weeks since I was given the offer and I'm still waiting on the background check to clear (I passed the management interview and drug test). I've heard little of nothing from the recruiter for two weeks and I now have another offer from another company. Can I back out of the first offer without consequences?
Yes, you may back out of this offer.
Having two offers gives you some power. It is good to use that power to advance your personal career. The best way to use that kind of power is subtly. To exaggerate, think "iron fist inside velvet glove." You can be polite without being weak.
The wise / subtle thing is to give the first employer a last chance to get their act together. Call your point-of-contact in the company (not the recruiter unless she is a company employee), and say, "You gave me a contingent offer on --date--, and I haven't heard anything since --date--. I have another job offer in hand, and I need to get to work. When can I expect you to complete your background check so I can start working for you?"
You can expect a professional and clear response to your question, and you can decide whether it meets your needs. If you don't get a clear response, or it doesn't meet your needs, move on to the other job.
The first company will know why they lost you. That's what you will want when you are a hiring manager one day. (They'll finish background checks on time on your watch!)