I'm just going to leave this right here for everyone who has been talked into giving Omeprazole to their horse by their vet....
Side Effects from Omeprazole (healthfully.com)
ALL drugs have side effects. Research all drugs carefully before you use.
There are natural answers for most issues out there, They just may not be "quick and easy". If it's not immediately life threatening, try natural FIRST. A change of diet and Tummy B Calm can take care of MOST digestive issues.