Metformin

Where metformin fits in type 2 diabetes

Metformin, as metformin hydrochloride, is a biguanide — the tablet most people with type 2 diabetes start on, and it works alongside other treatments, insulin included. It cuts the glucose the liver releases between meals and overnight, reduces the glucose absorbed from food, and helps muscle respond to the insulin the body already makes. It does not push the pancreas to release extra insulin, so it rarely causes low blood sugar on its own. Ten metformin products are on this page: plain tablets, slow-release tablets and five combinations.

Plain tablets: 500mg, 850mg or 1000mg

Glucophage and the plain Metformin tablets are the same medicine under two names, each in 500mg, 850mg and 1000mg, and Glycomet is a third brand at 500mg. These are taken with meals two or three times a day, so the total is split across the day. A strength is a size, not a schedule: 500mg twice daily and 1000mg twice daily are different days. Doses usually move up a step at a time, which is easier on the stomach.

One tablet with the evening meal

Glucophage SR 500mg and Glucophage Xr 1000mg are extended-release tablets: one a day with the evening meal, swallowed whole rather than crushed or chewed. The medicine inside is the same; what changes is how often you take it and how the dose is spread through the day. If a midday tablet is the one you keep forgetting, a single evening dose is the simpler shape of day.

Combinations that add a second medicine

Istamet pairs metformin with sitagliptin at 50/1000mg, and Kombiglyze XR pairs it with saxagliptin in extended-release 5/500mg and 5/1000mg tablets. Glucovance and Metformin + Glyburide both pair it with glyburide, each in two strength pairs, and Actoplus Met adds pioglitazone at 500/15mg. Each of these already contains metformin, so it replaces plain tablets rather than joining them. Glyburide makes the pancreas release insulin whatever the sugar level, so low blood sugar is the risk with those two tablets. Pioglitazone makes fat, muscle and liver tissue more sensitive to insulin and can make the body hold fluid, so swollen ankles or a sudden weight gain are a sign to note.

What to watch for

Loose stools, nausea, stomach cramps and a metallic taste are common, worst in the first week or two. Metformin is cleared by the kidneys, so poor kidney function lets it build up towards lactic acidosis, a rare but serious reaction: extreme tiredness, deep or rapid breathing, stomach pain, muscle aches and cold hands and feet need urgent treatment. Vomiting, diarrhoea, fever, a serious infection or heavy drinking raise that risk. An operation or a scan with iodine contrast dye means a pause and a restart at least 48 hours later. Acetazolamide, topiramate and zonisamide add to the risk, and cimetidine raises metformin levels. Long-term use can leave vitamin B12 low. Keep the tablets dry and out of the heat.