Type 2 diabetes medicines: how the main options work

Metformin: usually the first medicine

For most people, metformin is the first medicine offered. It works mainly by reducing the amount of glucose the liver releases and helping the body respond better to its own insulin, rather than forcing extra insulin out. A useful feature is that, used on its own, it does not generally cause low blood sugar (a "hypo") and tends not to lead to weight gain. The commonest side effects are tummy related — nausea, loose stools or wind — and these often settle if the medicine is built up slowly or a slow-release form is used, ideally taken with food. Metformin has a long track record and remains the backbone of treatment for many.

Newer classes: SGLT2 inhibitors and GLP-1 medicines

Two newer families have changed the picture. SGLT2 inhibitors work in the kidneys, causing some excess glucose to pass out in the urine. GLP-1 receptor agonists act on the body's own appetite and blood-sugar hormones, lowering glucose and often helping with weight. What makes them stand out is that, in people at risk, several of these medicines have been shown to protect the heart and kidneys — reducing problems such as heart failure, kidney decline and cardiovascular events — beyond their effect on blood sugar alone. For this reason they are often chosen early when someone also has heart disease, heart failure or kidney disease, not just to improve glucose numbers.

Other options: DPP-4 inhibitors, sulfonylureas and insulin

Several other medicines have their place. DPP-4 inhibitors gently boost the body's own blood-sugar hormones; they are generally well tolerated and weight-neutral, with a low risk of hypos. Sulfonylureas, such as gliclazide, work by prompting the pancreas to release more insulin; they are effective but can cause low blood sugar and some weight gain. Insulin itself may be needed if other medicines are not enough, or in particular circumstances; it is very effective at lowering glucose but, like sulfonylureas, can cause hypos and weight gain. Treatment often combines medicines from different families so their effects add up, with the mix adjusted over time as your needs change.

Hypos and sick-day rules: knowing the differences

The risk of low blood sugar (a hypo) differs by medicine, and this matters for daily life. Metformin, SGLT2 inhibitors, GLP-1 medicines and DPP-4 inhibitors used on their own do not usually cause hypos. Sulfonylureas and insulin can, so if you take these you should know the symptoms — shakiness, sweating, confusion, hunger — and how to treat them. There is also an important "sick-day" point with SGLT2 inhibitors: if you become acutely unwell, cannot eat or drink normally, or are dehydrated, you may be advised to pause them temporarily, as continuing can occasionally trigger a serious problem. Ask your clinician for your personal sick-day plan, and never ignore feeling very unwell.

Individualised treatment and lifestyle

There is no single "best" medicine for everyone. Your clinician weighs up your blood sugar, weight, kidney function, heart health, risk of hypos and your own preferences, then tailors treatment to you — which is why two people with type 2 diabetes can be on quite different combinations. Treatment is also reviewed and changed over time as the condition and your circumstances evolve. None of these medicines replace the value of lifestyle: a healthier diet, regular activity, weight management and not smoking improve blood sugar and overall health, and can sometimes reduce the medicine needed. Medicines and lifestyle work best together, as part of a plan you build with your clinician.