Amazon.com Inc. must face a lawsuit alleging the e-commerce giant negligently sold a substance multiple teenagers used for suicide after a federal appeals court reinstated the claims Thursday.

The US Court of Appeals for the Ninth Circuit rejected Amazon’s argument that a product must be defective before a seller can be liable under the Washington Product Liability Act. Therefore, the lower court improperly dismissed common law negligence claims, the appeals court said in an unpublished opinion.

The lawsuit, brought under the WPLA, followed a rash of teen suicides that were linked to sodium nitrite purchased on Amazon. The plaintiffs argued …