The star was arrested by Swedish police after his car was pulled over in a roadside control in July. Earlier in the evening he had given a concert in the university town of Uppsala, north of Stockholm.
He denied on social media that he had been taking drugs, but tested positive for narcotics in a preliminary test, said police.
Investigator Magnus Hänström told public broadcaster SVT late on Thursday that a final conclusive analysis by Sweden's National Forensic Centre has now strongly indicated drug use.
“The findings showed the highest measurable value,” he said.
However, the investigation has been dropped without charges.
“Even if he turned out to be under the influence of narcotics, we don't know if he has consumed it on Swedish soil. That would be a precondition for prosecution in cases like this,” said Hänström.
According to police in Uppsala, Snoop Dogg, also known as Cordozar Calvin Broadus Jr, said he had taken the narcotics in the US, where it unlike in Sweden is legal in certain states to smoke drugs such as cannabis.
“He had a prescription which he showed at the time, which gives him permission to buy and use narcotics in some states,” Hänström told SVT, which said it had contacted Snoop Dogg for a comment.
“We did not find any narcotics on him,” he added.
Snoop Dogg's song lyrics often display his fondness for marijuana and he has previously had run-ins with police elsewhere over the drug.
However, the singer hit out at Swedish police at the time of his arrest, complaining that it was due to racial profiling, which police denied. He also vowed never to return to Sweden.
Sweden has by and large a 'zero tolerance' approach to drugs, although calls for legalizing the drug are sometimes heard. The Nordic country criminalized illicit drug use in 1988, following a two-year attempt to introduce a more tolerant approach that was considered a failure by authorities.