What your diabetes medicines actually do
Four tablets from four different classes, each working on a different organ by a different mechanism. Knowing which is which changes what you watch for.
Most patients arrive able to name their tablets by colour and size, and almost none have been told what any of them does. That matters, because what you should watch for depends entirely on the class — and because a patient who understands why a medicine is there is far more likely to keep taking it.
Metformin
The most prescribed, the oldest, and the one most often wrongly feared. It works mainly by reducing the glucose the liver releases and by improving the body's response to its own insulin. It does not force insulin out, so on its own it does not cause low sugar. It does not damage kidneys. Its common problems are abdominal — loose stools, nausea, a metallic taste — which the extended-release form and taking it with food usually settle. Over years it can lower vitamin B12, which is one of the quietest causes of tiredness and tingling in a diabetic patient.
The sulfonylureas
Glimepiride, gliclazide and their family press the pancreas to release insulin whether blood sugar is high or not. They work quickly and they are cheap, which is why they are everywhere. The consequence is that they can drive sugar too low — particularly if a meal is missed, during Ramadan, in the elderly, or where kidney function has declined — and they tend to add weight. If you take one, you should know what a low feels like and what to do about it before it happens.
The newer classes
- DPP-4 inhibitors — sitagliptin and relatives. Modest effect, well tolerated, little risk of lows.
- SGLT2 inhibitors — empagliflozin, dapagliflozin. Work by passing glucose out in the urine; also protect heart and kidneys. Watch for genital and urinary infection, dehydration, and a rare but serious ketoacidosis that can occur at near-normal sugar levels.
- GLP-1 agonists — injected weekly or daily. Strong effect on weight and sugar. Nausea is common early; they are not a cosmetic weight-loss product and are not for unsupervised use.
- Insulin — not a last resort and not a failure. Sometimes the right medicine from the start, and in type 1 diabetes it is not optional.
Why the class decides the advice
Two patients with the same HbA1c get different instructions depending on what is in their hand. One on metformin alone can safely be told to eat less and walk more. The same instruction to a patient on insulin and a sulfonylurea, without a dose review, is advice that can put them in hospital. This is the single most important reason to bring the actual boxes to a consultation rather than a list of names.
Where natural supplements sit in this
Alongside, with the interactions checked, and never instead. Some natural preparations lower blood sugar on their own; taken on top of a sulfonylurea or insulin without the dose being reviewed, that is not a bonus, it is a hypoglycaemia risk. This is exactly why the clinic will not dispense without a consultation and the full medicine list in front of it.
Do not stop, swap or change the dose of any prescribed medicine on your own, including on the strength of good readings. Bring every box, including anything you started and stopped, and anything bought without a prescription.
Questions people ask
- Does metformin damage the kidneys?
- No. Metformin does not cause kidney damage. It is cleared by the kidneys, which is why the dose is reduced or the drug stopped when kidney function falls below certain thresholds — a precaution about accumulation, not evidence of harm. The confusion is common and leads patients to stop a medicine that is protecting them. Longer-term metformin use can lower vitamin B12, which is worth testing for.
- Which diabetes medicines can cause dangerously low sugar?
- Principally insulin and the sulfonylureas — glimepiride, gliclazide, glibenclamide and their relatives — because they push insulin out regardless of what blood sugar is doing. Metformin, DPP-4 inhibitors and SGLT2 inhibitors rarely cause hypoglycaemia on their own. If you take a sulfonylurea or insulin and skip a meal, the risk is real.
- Are sugar-free sweeteners safe for diabetics?
- They do not raise blood sugar in the way sugar does, which is their purpose. They are not, however, a reason to eat more of the food they are in, and the evidence on some of them and on appetite and gut bacteria is not settled. A sugar-free sweet biscuit is still a biscuit made of refined flour.