Eli Lilly will buy privately held SiteOne Therapeutics in a deal worth as much as $1 billion, the companies said Tuesday, giving the drugmaker access to an experimental non-opioid pain medicine.

SiteOne's STC-004 belongs to a class of drugs, known as Nav1.8 inhibitors, that targets the channels involved in transmitting pain signals.

Vertex Pharmaceuticals' recently approved non-opioid painkiller Journavx also belongs to the same class.

Under the terms of the agreement, SiteOne shareholders could receive up to $1 billion in cash, inclusive of an upfront payment and subsequent payments upon achievement of certain regulatory and commercial milestones.