This graph shows a comparison between Sertraline 100mg 28 and Sertraline 50mg 28.
The average UK prices of both packs fell after the generic launch in Feb 2012 to under £1. By November 2012 the average prices of both UK packs started to rise dramatically. In April 2013 Sertraline 100mg 28 reached £25.40 and Sertraline 50mg 28 £14.48 which explains the introduction of the Concession price. Both packs then fell to the £1 mark again in Feb 2014 and continued to stay at around this point until June 2020 when the 100mg reached £12.31 and the 50mg reached £7.42. Price concessions were granted both packs when prices peaked in 2011, 2013, 2019, and 2020.
There seems to be a pattern in that these products do seem vulnerable to price rises, and as two such incidents have been seen, there is every likelihood that it will occur again.