The euro's strength against the pound has made the company less able to compete on price, and last year's bad summer made it difficult to recruit new cider drinkers, C&C said.
The group is reorganising its Irish operations and expects to cut its 120-strong workforce in Clonmel.
But it hopes to take advantage of deflation in media costs and grow sales, notably for its recently launched pear variant.
Group chief executive John Dunsmore said: "In the course of the next 12 months we expect to make major progress on cost competitiveness and move to make the business leaner and faster to react to market-led changes. The key task is to create a sustainable and secure platform for our cider business in Ireland and the UK. This will ensure that we build a strong foundation for growth in future years."