The company disclosed the tentative settlement last November.
Cephalon said Monday it also would pay an estimated $12 million in interest.
One of the drugs, Actiq, was marketed for maladies including migraines and injuries when the fentanyl lollipop is a highly addictive narcotic approved only for certain cancer patients, authorities said.
Doctors can prescribe drugs for uses other than what has been approved by the U.S. Food and Drug Administration, but pharmaceutical companies cannot promote such "off-label" marketing.
The Frazer, Pa.-based company has signed an agreement to plead guilty to one count of distribution of misbranded drugs.
Cephalon also marketed Gabitril, an anti-epilepsy drug, for anxiety, insomnia and pain, authorities said.
Provigil, which is approved for narcolepsy, was marketed for fatigue, among other things, authorities said.
Cephalon also announced it agreed to pay $6.15 million to Connecticut and $700,000 to Massachusetts to settle related investigations.
