The Nevada State Athletic Commission recently informed MMAmania.com that all 12 of the fighters randomly tested for drugs on the UFC 81: "Breaking Point" fight card on February 2 from the Mandalay Bay Events Center in Las Vegas, Nevada, came back negative.

Here's the list:

• Timothy Sylvia
• Antonio Nogueira
• Brock Lesnar
• Frank Mir
• Nathan Marquardt
• Jeremy Horn
• Rob Emerson
• Tim Boetsch
• Tyson Griffin
• Marvin Eastman
• Ricardo Almeida
• Chris Lytle

Fighters are tested for banned substances such as performance-enhancing anabolic steroids, as well as recreational drugs like marijuana and cocaine.

There's no tried and true reason behind the selection process -- six fighters were not required to submit samples for testing. However, it's customary that state athletic commissions screen the marquee fighters at the very least.

For complete UFC 81 fight coverage click here and here.