Story highlights Some law enforcement officials say the rise in synthetic marijuana is leading to more crime

Overdoses are also on the rise, according to reports

(CNN) Synthetic marijuana is flooding the streets of major U.S. cities this summer, causing a surge in overdoses and, according to some police officials, a rise in violent crime.

The situation has become urgent enough that police chiefs meeting in Washington this week called for development of field tests that can help police quickly figure out suspects on the synthetic marijuana.

Sold in slickly marketed packets with names like K2, Scooby Snax and Spice, the drugs are made up of a variety of chemicals and have little to do with marijuana.

The chemicals found in the packets vary -- even identically branded packages often contain vastly different ingredients -- and users likely have no idea what they're smoking.

By early July, poison control centers in the U.S. tallied 4,377 reports of people suffering the effects of synthetic marijuana, compared to 3,682 in all of last year, according to the American Association of Poison Control Centers.

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