By Sriparna Roy

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

SiteOne's STC-004 will help Lilly expand its pipeline of drugs for chronic pain conditions such as migraine, as the pharma giant strives to get ahead in the race for alternatives to addictive opioid painkillers.

STC-004 belongs to a class of drugs known as Nav1.8 inhibitors that targets the channels involved in transmitting pain signals. Opioids, on the other hand, trigger the brain's reward centers as they travel through the blood and then attach to neural receptors, leading to addiction and abuse.

Vertex Pharmaceuticals' recently approved non-opioid painkiller Journavx is also a Nav1.8 inhibitor.

Lilly's wider pain profile includes experimental drugs for diabetic peripheral neuropathic pain and to treat nerve pain that begins in the feet and moves up the leg to just below the knee.

The SiteOne deal extends Lilly's trend of diversification beyond its recent success in obesity into therapeutic areas that the company knows well, said BMO Capital Markets analyst Evan Seigerman.

Under the deal terms, SiteOne shareholders could get up to $1 billion in cash, including an upfront sum and subsequent payments when certain regulatory and commercial milestones are met.

SiteOne is also studying other experimental drugs to treat conditions including pain and cough.

For years, drugmakers have been trying and failing to bring new alternatives to opioid painkillers that have fueled a national addiction crisis in the U.S.

Lilly and partner Pfizer discontinued the development of another non-opioid experimental drug, tanezumab, in 2021 after regulatory setbacks.

In 2023, Lilly signed a deal with Confo Therapeutics to license its experimental non-opioid drug for neuropathic pain, a condition caused by damage to the nerves outside the brain and spinal cord.

(Reporting by Sriparna Roy in Bengaluru; Editing by Devika Syamnath)