The new pills contain the highly addictive painkiller hydrocodone, packing up to 10 times the amount of the drug as existing medications such as Vicodin. Four companies have begun patient testing, and one of them — Zogenix of San Diego — plans to apply early next year to begin marketing its product, Zohydro.

If approved, it would mark the first time patients could legally buy pure hydrocodone. Existing products combine the drug with nonaddictive painkillers such as acetaminophen.

Critics say they are especially worried about Zohydro, a timed-release drug meant for managing moderate to severe pain, because abusers could crush it to release an intense, immediate high.