Next to HbA1c, body weight is regarded as an important surrogate end-point in trials investigating glucose-lowering agents. An increase in weight could contribute to worsening insulin resistance. Differences in weight after starting glucose lowering agents have been described in many randomized controlled trials (RCTs).

With this prospective observational study, weight trajectories after receiving add-on therapy next to metformin are evaluated in primary care patients with good glycaemic control.

This prospective cohort study is part of the ZODIAC (Zwolle Outpatient Diabetes project Integrating Available Care) study, which started in 1998 as a prospective observational study and includes patients with known T2DM who are treated in primary care.

The investigators aim to investigate the course of the bodyweight and glycaemic control, the years after starting specific SU's, pioglitazone or insulin as add-on therapy, in metformin treated primary care patients with T2DM.

As part of the process called benchmarking, a dataset of quality measures is collected annually for all patients participating in the ZODIAC study during the patient's visit to the practice nurse and/or general practitioner and sent to the investigators' diabetes centre for benchmarking and research purposes once a year.

Inclusion Criteria:

• T2DM
• Treated in primary care in period 1998 to 2012
• used metformin monotherapy
• subsequently received add-on therapy with a SU or pioglitazone during their entire follow-up period

Patients with T2DM who received monotherapy with metformin and needed treatment intensification by receiving add-on therapy next to metformin