Magners sales were down 10.4% with volumes hit by reduced share of promotional deals in supermarkets.
The company said in a statement on its financial results that Magners “remains in good health” and that it was supporting the brand with marketing investment “equating to a very competitive double digit percentage of net sales revenue”.
It added that it would “continue to invest in the brand while reducing operating costs to stabilise margin”.
Sales of Gaymers products dropped 19.3% over the period due to the impact of rival fruit-flavoured brands.
C&C’s Tennent’s lager business in Scotland saw revenue drop 4.6% but operating profits rose 9.2%.
Chief executive Stephen Glancey said: “Tennent’s provides a degree of balance to a competitive UK cider market.
“While Magners volume performance improved in the second quarter, fundamentals in the UK cider market remain challenging.
“While early days, we are beginning to make progress with both the Addlestones and Blackthorn brands.
“A broader cider portfolio will be a distinguishing factor for C&C in the evolution of the cider market in the UK and Ireland.”