Washington ? Rats can become drug addicts.

That’s important to know, scientists say, and has taken a long time to prove. Now two studies by French and British researchers show the animals exhibit the same compulsive drive for cocaine as people do once they’re truly hooked.

Only through experiments with addicted animals can scientists eventually learn what makes some people particularly vulnerable to addiction while others can quit at will, addiction specialists say.

Addicted rats also could help uncover new anti-drug therapies.

Until now, scientists have been able to prove that rats will take drugs, even eagerly, but not that they’re actually addicted. The new research was published Thursday in the journal Science.

“What confers susceptibility to experimenting and trying drugs may be quite different than what changes your brain and leads to addiction,” explained Terry E. Robinson, a University of Michigan neuroscientist. “These articles provide us the approaches and the techniques to ask the latter.”

“There’s some fundamental shift” between casual drug use and addiction, added David Shurtleff, chief of basic neurological research at the U.S. National Institute on Drug Abuse. “Your brain has changed and that’s manifest as a change in behavior. … That’s something new that’s never really been nailed down in an animal model.”

Among the ways to know when a rat’s hooked: It keeps trying to get cocaine even when each hit comes with an electric shock.

Compulsive drug-seeking even in the face of bad consequences is a measure of human addiction.