I have fairly infrequent bouts of IBS and found that no tablets were very effective. Then my GP went to a conference and was shown a video where peppermint oil was sprayed directly into the bowel of a woman patient. He said you could see the inflammation disappearing. He then prescribed Mintec capsules for me which contain peppermint oil and they do the trick. They are coated to stop them dissolving before they reach the bowel and this makes them more effective. If you buy peppermint oil capsules over the counter which are not coated they are not as efficient. Look for the word 'enteric' on the label.
I hope this helps.