Metformin in Australia: A Doctor’s Review of the Time-Tested Metabolic Guardian

From the consulting room of an Australian GP — written for Australians over 30 who want to protect their energy, brain, bones and future.

A — Attention: The Silent Metabolic Drift After 30

If you are over 30, you may have noticed it already: the waistline is harder to shift, energy dips after meals, brain fog creeps in, and your blood tests show “borderline” glucose. Perhaps diabetes or prediabetes runs in your family. Perhaps you are frightened of the long-term complications of high blood sugar — nerve damage, vision loss, kidney failure, heart attack, even amputation.

Here is the truth many patients are not told: the metabolic slide often starts years before a formal diabetes diagnosis. The good news? One of the safest, cheapest, and most studied medicines in Australia has been protecting metabolic health for decades. That medicine is metformin.

Metformin is not a fad. It is not expensive. It is not a new “wonder drug” with unknown risks. It is a PBS-listed, first-line treatment for type 2 diabetes, and it is increasingly discussed for prediabetes, polycystic ovary syndrome (PCOS), and healthy ageing. If you are tired of feeling run-down by blood sugar swings, metformin may deserve your attention.

I — Interest: What Exactly Is Metformin?

Metformin belongs to a class called biguanides. It works mainly by reducing the liver’s excess glucose production and improving the body’s sensitivity to insulin. This means less sugar flooding your bloodstream, more stable energy, and less strain on your pancreas. It does not cause weight gain, and for many people it helps with modest weight stability or loss. In Australia, common brands include Glucophage, Diabex, Diaformin, and Formet.

D — Desire: Why I Prescribe Metformin — Answers to Your Real Questions

Here are the questions my patients ask most often — and the answers that make metformin a valuable tool in your metabolic armoury.

What is the half-life of metformin?

Metformin has a plasma half-life of about 6.2 hours. It is not metabolised by the liver — instead, it is excreted unchanged by the kidneys. This is important: it means metformin does not build up in the body in the same way as many other medicines, but it also means that if your kidney function is significantly reduced, your doctor may need to adjust the dose or use an alternative. For most people with healthy kidneys, twice-daily dosing keeps blood levels steady and effective.

Can metformin cause drowsiness?

Drowsiness is not a typical direct side effect of metformin. If you feel unusually tired or sleepy while taking metformin, do not ignore it. Possible causes include:

• Vitamin B12 deficiency — long-term metformin can reduce B12 absorption, which may cause fatigue and nerve symptoms.
• Blood glucose too high or too low — metformin alone rarely causes hypoglycaemia, but if combined with other diabetes medicines, low sugar can make you drowsy.
• Poor sleep, sleep apnoea, or underlying anaemia — common in the over-30 age group.

If you feel drowsy, see your doctor for a simple blood test. The tiredness is often fixable, and metformin is rarely the sole culprit.

Should you stop metformin during a fast?

This depends on the type of fast. For intermittent fasting or a short overnight fast, metformin can usually be continued — but take it with food when you do eat. For prolonged or water-only fasts, you should speak with your doctor. Because metformin lowers liver glucose output, it does not typically cause dangerous hypoglycaemia on its own, but if you are not eating for more than 24 hours, you may feel lightheaded or unwell. For religious fasts such as Ramadan, many Australian patients can continue metformin with careful timing — but individual advice is essential. Never stop or change a prescription medicine without consulting your GP.

Metformin and elective surgery: when to hold?

This is one of the most important safety questions. As a rule, metformin should be withheld on the day of surgery. If you are having a procedure that requires prolonged fasting, or if you are receiving contrast dye for imaging, your anaesthetist or surgeon may advise holding metformin for 24–48 hours beforehand, especially if your kidney function is borderline. The goal is to reduce the rare risk of lactic acidosis during periods of dehydration or reduced kidney perfusion. You can usually restart metformin once you are eating normally and your kidney function is stable — often 48 hours after surgery. Always tell your surgical team you take metformin.

What is the evidence for metformin in ageing?

This is where metformin gets genuinely exciting. Metformin activates AMP-activated protein kinase (AMPK), a cellular energy sensor linked to longevity pathways. It also reduces insulin resistance, lowers inflammation, and may influence epigenetic ageing. Large observational studies in people with type 2 diabetes have shown that metformin users often have lower risks of cardiovascular events, cancer, and all-cause mortality compared with users of other diabetes medicines. The landmark TAME (Targeting Aging with Metformin) trial is now testing whether metformin can delay age-related diseases in non-diabetic adults. It is not yet approved as an “anti-ageing” drug in Australia, but the metabolic evidence makes it one of the most promising medicines for healthy ageing.

What to do with expired metformin?

Do not use expired metformin. Once a medicine passes its expiry date, its potency can decline, and the breakdown products may not be safe. In Australia, you can return expired or unwanted medicines to any pharmacy through the Return Unwanted Medicines (RUM) project for safe disposal. If your metformin is expired, do not flush it down the toilet or throw it in household rubbish. Ask your pharmacist, and if you need a new script, book a GP appointment.

Should metformin be taken with food?

Yes — take metformin with or immediately after food. This is one of the simplest ways to reduce the stomach upset, nausea, and diarrhoea that some people experience in the first few weeks. Start low and increase the dose gradually. The extended-release (XR) version is often taken with the evening meal and may be gentler on the gut. Taking it with food also helps you remember the dose as part of a daily routine.

Metformin and bone density: any effect?

Many patients worry that medicines for chronic conditions weaken bones. The good news for metformin: it does not increase fracture risk, and it may actually be bone-neutral or bone-protective. Preclinical studies suggest metformin can stimulate bone-forming cells (osteoblasts) and reduce the formation of advanced glycation end-products that damage bone quality. In people with type 2 diabetes, some studies have found stable or even improved bone mineral density with metformin compared with other diabetes drugs. So if you are over 50 and concerned about osteoporosis, metformin is not a threat to your bones — and it may be a quiet ally.

A — Action: Your Next Steps

Metformin is not a miracle pill, and it is not for everyone. But if you are over 30, carrying extra abdominal weight, struggling with prediabetes or type 2 diabetes, or simply want to protect your long-term metabolic and cognitive health, metformin deserves a serious conversation with your GP.

Here is what I suggest you do today:

• Book a GP appointment and ask for a comprehensive metabolic check: fasting glucose, HbA1c, kidney function, liver function, B12, and a cardiovascular risk review.
• Ask your GP directly: “Is metformin appropriate for my blood sugar, my weight, and my long-term health?”
• If prescribed, start low and slow, take it with food, and give your body two to four weeks to adjust.
• Return expired medicines to your local pharmacy and keep your medicine list up to date.

In Australia, metformin is one of the most affordable, PBS-listed medicines available — often costing just a few dollars for a script. That is remarkable value for a drug with decades of safety data, a strong metabolic track record, and growing evidence for healthy ageing. If you want to take control of your energy, your brain, your bones, and your future, metformin may be the simple, proven tool you have been missing.

This article is for general educational purposes and does not replace individual medical advice. Always discuss any medication changes — including stopping, starting, or adjusting metformin — with your Australian GP or specialist.