A synthetic marijuana product maker won reversal of a $24.5 million judgment when a Florida appeals court said it can’t be held liable for a fatal car wreck caused by a driver who misused a product and became impaired.

The driver’s criminal conduct was the sole proximate cause of the deaths as a matter of law, the Florida Court of Appeal said.

DZE Corp. manufactured products containing synthetic marijuana known as “spice,” a highly dangerous chemical marketed as “potpourri,” the court said. The potpourri was labeled, “Not for human consumption,” the court said.

Christopher Generoso voluntarily consumed it, became impaired,…