I was on Januvia for a short period (about two months) without any problems. It was very effective in getting my sugars under control. However I did ask yo go on Metformin only ( one of the two active substances in Januvia, the other being sitagliptin). Metformin is an "old" medicine with s known history of being safe. Sitagliptin is much newer and I preferred not to take s chance with it if I could manage without. There is a rumored additional benefit to Sutaglyptin as it is claimed to protect beta cells from further deterioration, but I am not sure if this claim has been proven.
A diabetic friend has been on januvia for about three years now, with no adverse side effects.
Pavlos