PASADENA (CBSLA) — California Highway Patrol has already started its maximum enforcement for the holiday weekend — and they’re not just looking for drivers under the influence of alcohol.

“With folks who are under the influence of narcotics or marijuana, they tend to react slower, the way they turn the steering wheel, the way they apply the brakes,” CHP officer Vince Ramirez said.

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Drivers who are under the influence of marijuana face the same penalties as those driving under the influence of alcohol. And this year, Ramirez said CHP officers are cracking down on both — though it can be tricky.

“With marijuana for example, we look at the eyes,” he said. “We listen to the way they speak, a lot of times they have slurred speech or slower speech.”

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For any driver suspected of being under the influence, Ramirez said they will be taken into custody at the checkpoint and field sobriety tests will be conducted. If a driver is suspected of being under the influence of something other than alcohol, the driver is taken to a hospital for a blood test.

“If they decline the blood test, then they lose their license for a year,” Ramirez said. “In cases where somebody committed a serious crime, say a DUI crash, there is a way to get the blood through a warrant.”

Since the legalization of recreational marijuana last year, CHP has trained officers to be Drug Recognition Experts so they can spot the signs that a driver is under the influence of drugs. But, because there’s no legal limit for marijuana like there is for alcohol, the prosecution becomes more of a challenge.

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The increased enforcement lasts through Monday night.