SAN FRANCISCO  Reacting to what it called complaints from law enforcement and a surge in medical emergencies, the Drug Enforcement Administration said on Wednesday that it would ban several chemicals used to make so-called synthetic marijuana products, which resemble herbs or potpourri but mimic the effects of the drug when smoked.

In a notice published in the Federal Register, the agency said it would use its emergency powers to ban possession and sale of five synthetic cannaboids whose effects mirror that of tetrahydrocannabinol, or THC, which gives marijuana its potency. Those chemicals are used to coat a variety of products which are marketed as incense, but have become popular as smokables for those seeking a legal high.

Under the action, the five cannaboids will be listed as Schedule I substances, the most restrictive category, for at least a year while the government studies whether they should be permanently banned.