So, yes. Viagra can cause GI side effects. Here are the ones listed on the RX website: stomach pain,
upset stomach, nausea, diarrhea. Indigestion, or heartburn, is a common side effect of Viagra. This occurs because of the effects of Viagra on smooth muscle tissue in your body. That's how it helps with erection but it carries over to the digestive tract as well, unfortunately. Talk to your doctor about it!