I was on Sitagliptin for 2 years with no side effects other than slight headache in the first week. It does have some side effects for a small number of users - read the leaflet. The Gliptin family are DPP-4 inhibitors. They work by inhibiting an enzyme that in turn switches off the beta cells a certain time after a meal. The result is that insulin is produced for a longer after a meal. They should work within a day or two and don't need to build up. Note that the Glipins only reduce spikes and nothing else. The sulfonylureas such as Gliclazide are the tablets to be used to increase the overall beta cell output if that is needed.