Four shops in Minnesota have filed a lawsuit against the US Justice Department and the Drug Enforcement Administration (DEA) over a federal ban on five chemicals commonly found in a blend of legal herbs many have used as a synthetic form of marijuana.

The DEA announced in November that it would use its emergency powers to place five synthetic cannabinoids into Schedule I of the Controlled Substance Act (CSA), a category reserved for substances with no accepted medical value and a high potential for abuse. The five substances are: JWH-018, JWH-073, JWH-200, CP-47,497, and cannabicyclohexanol.

Herbal blends containing the chemicals were commonly sold as incense and marketed under the names K2, Spice, Yucatan Fire, Skunk and others. Like the main active substance in marijuana, tetrahydrocannabinol, the five substances bind to cannabinoid receptors in the brain.

The emergency ban was to last for at least one year while the DEA and the United States Department of Health and Human Services study whether the substances should be permanently controlled.

The lawsuit claimed the ban is unconstitutionally vague because under the Federal Analog Act, a section of the CSA, any chemical substantially similar to one of the five synthetic cannabinoids would also be illegal to possess.

"No person of normal intelligence would be able to determine what is, and what is not illegal," the lawsuit states.

The lawsuit additionally alleged that the DEA's use of its emergency scheduling authority to temporarily control five substances violated the Congressional Review Act and Regulatory Flexibility Act.

"The DEA has overstepped its bounds by taking over the acts of Congress without sufficient scientific evidence or support," Marc Kurzman, the attorney representing the shops, told Pioneer Press. "We're arguing that the government should not be above the law."

"Without scientific research, we think it's premature to turn tens of thousands or millions of people into felons overnight," he said. "We prefer the regular rulemaking. It's the whole process of due process."

The owners of Last Place on Earth, Down In the Valley, Disc and Tape and Hideaway LLC said that they derive at least 50 percent of their profits from the sale of products containing one or more of the five synthetic cannabinoids. They are seeking an injunction and temporary restraining order banning enforcement of the new law.

"I just don't see them taking this product that I think is less harmful than alcohol, less harmful than prescription pills and banning this when cigarettes and alcohol and everything else is legal," the owner of Last Place on Earth told WDIO. "I don't think it's right for them to take this away from a percentage of people."

Smoking JWH-laced herbal blends has been linked to numerous severe reactions around the United States, with large doses triggering hallucinations, rapid heart rates, vomiting and in extreme cases, seizures.

It has not been shown to be carcinogenic or cause long term health problems, but numerous countries in the European Union have already banned the substances.