Merck & Co’s decision to suspend sales of its Zilmax cattle feed additive has caused such a surge in demand for rival Eli Lilly & Co’s Optaflexx that Lilly is telling some new customers it cannot immediately supply them, some US-based customers have told Reuters.

Eli Lilly & chief executive John Lechleiter said rising sales of the antidepressant Cymbalta and animal drugs stemmed losses from generic competition, helping the company’s earnings beat estimates.