The U.S. Drug Enforcement Administration is in the final stages of scheduling three synthetic cannabinoids as Schedule I substances.

The DEA proposes placing the chemical compounds AB-CHMINACA, AB-PINACA and THJ-2001 under Schedule I classification of the U.S. Controlled Substances Act, according to proposed rulemaking filings made public Thursday and published Friday on the Federal Register. As the rulemaking process progresses, the DEA also is extending a temporary ban issued in 2015 for the three substances that have been linked to “multiple deaths and severe overdoses” since 2013, according to the filings.

The three synthetic cannabinoids and related substances — sometimes referred to as Spice, K2 and various other names — are designed to mimic the effects of marijuana, but possess greater danger as they’re higher in dependence potential and potency, according to the DEA and the U.S. Department of Health and Human Services.

The chemicals, which are not derived from the cannabis plant, are sprayed onto dried plant matter and packaged for sale.

“Globally, synthetics are the No. 1 long-term drug threat: They are a favorite of drug traffickers worldwide because they are cheap and relatively easy to make, and can be produced anywhere,” Russell Baer, a DEA spokesman, wrote via e-mail to The Cannabist. “Deaths in the U.S. from psychostimulants (which includes meth) have increased from 1,302 in 2008 to 4,298 in 2014.”

The highly accessible and potentially deadly concoctions also have started to confound the courts, the Associated Press reported last week:

Those who make synthetic drugs can alter their chemical makeup faster than regulators can ban them, and those who sell them can skirt the law through misleading labeling.

Meanwhile, the DEA’s forensic testing laboratories are “overwhelmed with the amount of substances” they’re trying to identify and analyze, said spokesman Baer.

Amid concerns about consistency in punishment, the U.S. Sentencing Commission is doing a two-year study on synthetic drugs that, among other things, will look at whether to update the drug quantity table that federal judges rely on at sentencing.

Judges use the table to come up with the starting point for the sentence based on the amount of drugs involved, then factor in considerations like a defendant’s criminal history and level of responsibility.

“DEA is always concerned about the rise in new and emerging drug use and trafficking trends. We continue to identify a new psychoactive substance (could be a synthetic cannabinoid, cathinone, or opioid class substance) once every few weeks,” Baer said via e-mail. “Drug use and trafficking trends go in cycles: Our objective at DEA is to reduce their length and impact with aggressive enforcement and outreach.

“Right now, opioids are the substances causing the most damage to our country, but DEA is ever vigilant to emerging threats.”

A Schedule I classification — assigned to substances such as marijuana and heroin — indicates that the drug has a high potential for abuse, there’s no currently accepted medical use in the United States and there’s a lack of accepted safety under medical supervision, according to the DEA.

The comment period for the proposed rule for AB-CHMINACA, AB-PINACA and THJ-2201 extends until Feb. 27, 2017.