The Drug Enforcement Administration took emergency action on Friday to ban three synthetic stimulants used to make products that are marketed at head shops and on the Web as “bath salts,” but are actually used as recreational drugs that mimic the effects of cocaine, LSD and methamphetamine.

The emergency measure places these substances — mephedrone, methylenedioxypyrovalerone (MDPV) and methylone — under the D.E.A.’s most restrictive category for at least a year, while they study whether they should be permanently banned. This classification is reserved for substances with high potential for abuse and no accepted use under medical supervision.

These products, sometimes called plant food, are sold in powder or crystal form under names like Bliss, Purple Wave, Vanilla Sky and Ivory Wave. Though not approved by the Food and Drug Administration for consumption, they have become increasingly popular, especially among teenagers and young adults, the D.E.A. said.

“These chemicals pose a direct and significant threat, regardless of how they are marketed, and we will aggressively pursue those who attempt their manufacture and sale,” Michele M. Leonhart, the agency’s administrator, said in a statement.