Friends of Charlie Sheen's soon-to-be-ex-wife Brooke Mueller are worried that she relapsed into drugs!

The 33-year-old Mueller just made a round of phone calls to ask if they'd give her urine samples, RadarOnline.com has exclusively learned.

Mueller found out early Thursday that she'd have to report to a Los Angeles testing facility to provide a urine sample. So, about 6:15 a.m. PT, Mueller was frantically calling friends most likely to be "clean," babbling about not wanted to lose her kids and begging for their pee.