States have universally adopted a .08-percent blood-alcohol level as presumption of drunk driving, but no such standard exists for driving under the influence of other drugs. New Mexico, however, is seeking to establish guidelines that other states could emulate.

The Associated Press reported Feb. 19 that New Mexico Gov. Bill Richardson is backing a plan to establish blood-concentration levels for five illicit drugs as a legal presumption of intoxication. The drugs are marijuana, cocaine, heroin, amphetamine, and methamphetamine.

Supporters said the standards would be especially useful for when drivers mix alcohol and other drugs, since it can be difficult to prosecute offenders if their blood-alcohol level is below .08 percent. In New Mexico, 90 percent of drivers who failed field sobriety tests but had blood-alcohol levels below .08 percent tested positive for marijuana, researchers found.

Currently, many states consider any positive test for the presence of illicit drugs per-se evidence of impairment.