Stiefel Laboratories in Sligo has confirmed it is to close its manufacturing site in the town.
The closure will see 165 staff lose their jobs.
The facility will shut down on a phased basis over the next three years.
Workers were informed of the closure this morning.
Management at the skincare facility say they considered alternatives before making the decision, but were left with no other option.
They added that keeping the facility open would take significant investment, which would result in huge losses.
The company said they understand the impact the closure will have on employees, and will offer them all the support they can.
Parent company GSK (GlaxoSmithKline) says its other operations in Ireland are not impacted.
Stiefel Laboratories was taken over by GSK in 2009.
The Sligo site is said to manufacture "40 different formulations of skin healthcare products" for dozens of markets.
GSK has previously said it had "invested heavily in the site and its people to ensure that the infrastructure and capability delivers world class performance for the future".
