Because illicit substances only stay in the body for so long, Tameka Raymond has asked a judge to expedite the drug testing of her ex-husband, R&B crooner Usher, TMZ reports.

Raymond and Usher, who married in August 2007 and divorced in 2009, are in the midst of a bitter custody fight over their two children, Usher Raymond V and Naviyd Ely Raymond. The singer has thus far refused to take a drug test, insisting his baby momma's demands are "frivolous and unfounded," according to the gossip site.

Raymond is seeking strip her former hubby of joint custody rights, and last month, she accused him of violating numerous terms of their prior agreement. In particular, she charged that Usher traveled with the children outside of Georgia, hired nannies without consulting her, failed to make $5,000-per-month payments so that she might hire a nanny and -- perhaps most egregious of all -- took away her Saks 5th Avenue card.

Representatives for Usher have yet to comment.

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