Have a healing duodenal ulcer diagnosed a few weeks back. Need to take Lansoprazole to aid the healing (twice a day) for 6-8 weeks. Noticed in last few days diarrhoea (or my usual IBS symptoms getting worse)?
Have been on Lansoprazole a few months ago but only one pill a day and seemed OK
Certainly a known side effect. If you know you can tolerate a lower dose, might be worth having a word with your consultant/GP to see if they will officially sanction it.
PS PPIs have a relatively long effectiveness (a few days rather than hours like most medication), so that might be a persuasive argument to lower the dose.
If you're on Lansoprazole and have IBS you may want to read this....
Can Lansoprazole cause more harm than good if you have IBS? Is it better to be on them or off if you have suspected Gord?
Undiagnosed severe bloating after eating .2 months ago vomiting diarrhoea nausea stopped since taking lansoprazole. Endoscopy? 
Lactulose and side effects
IBS or Blockage?
