we switched to follow on milk and switched back after 5 days, didnt agree with lo at all, could just be a coinsidence but she ended with a bad stomach and awful nappies, pooing 5 times a day and it wasnt nice at all lol. we switched back and she was back to her normal self in a couple of days. Like i say could just be coinsidence, but first milk is fine till 1 year so im sticking to it.