Hello, Gabapentin, like many medications, is known to occasionally cause GI problems such as nausea and stomach upset, though it is not typically known for the loss of appetite. However, anytime there is a change in health like this, looking at medication changes is very reasonable, and I would consider trying to not use gabapentin for awhile to see if this makes a difference. Then you would know if you need to investigate other causes for his loss of appetite, or if you need to find another way of treating the neuropathy. Another possibility with diabetes is patients often develop gastroparesis, which is when the stomach does not digest and push the food along like normal, which often leads to a loss of appetite. You could talk to your doctor and see if trying a medication to help with stimulating the stomach to move better would be appropriate. Hope I have answered your query. Let me know if I can assist you further. Take care Regards, Dr Aaron Branch, General & Family Physician