Hi. Thanks for the query. Yes, Augmentin can cause diarrhea as it contains Amoxicillin as a main ingredient that is an antibiotics. It has a common gastric side effect to cause diarrhea but it is temporary and will get resolved once the medicine intake is stopped. If the loose motions or diarrhoea is not causing any discomfort and it is manageable then Augmentin should not be stopped, rather be continued. To reduce the side effects of the antibiotic, he should take plenty of probiotics in his diet like yoghurt and drink plenty of water.. Take soft meals and avoid spicy and heavy meals.. Omeprazole can be taken empty stomach till he is on antibiotics. If the symptoms worsen then please be brisk to consult an Emergency room.. Hope he feel better soon.. Regards.