You've been on metformin for six weeks. Maybe eight. The GP said it would help with the PCOS, possibly with weight — and you said yes because you were tired of feeling the way you felt, and metformin seemed like something concrete to try.
But here you are. The scale hasn't moved. Your energy feels about the same. The cravings are still there, loud and unreasonable, especially in the week before your period. You Googled "metformin not working PCOS" at 11pm last Tuesday.
The problem isn't metformin. The problem is that nobody told you what to watch for. Most women expect metformin to work like a diet pill — take it, lose weight, feel better. That's not what it does. And because the actual mechanism is indirect, subtle, and slow, most women decide it's not working and either stop taking it or feel quietly defeated while still taking it.
If you're in that position right now, this post is for you. Metformin is working differently from how you expect — and once you know what to track, you'll be able to tell whether it's actually doing its job.
What Metformin Actually Does in a PCOS/PMOS Body
Metformin is an insulin sensitiser. Not a fat burner, not an appetite suppressant (though the effects can feel that way eventually), and not a hormone balancer — except indirectly.
Here's the mechanism, as simply as possible.
Metformin works on two fronts simultaneously. First, it reduces hepatic glucose output — your liver produces less glucose overnight, which means your fasting insulin is lower when you wake up. Second, it improves peripheral insulin sensitivity — your muscle and fat cells respond better to insulin, so your body needs to produce less of it after meals to do the same job.
Lower insulin is the key to everything that follows. Here's why this matters specifically for PCOS/PMOS.
High insulin — hyperinsulinaemia — drives the ovaries to produce excess androgens, specifically testosterone. This is one of the core feedback loops in PCOS/PMOS: insulin resistance → high insulin → high androgens → irregular cycles, acne, hirsutism, and a further worsening of insulin resistance. It's a loop that feeds itself.
When metformin lowers insulin, it interrupts that loop. Lower insulin → lower androgen stimulation from the ovaries → gradually lower androgen effects. This is why some women notice reduced facial hair, clearer skin, and more regular cycles before they see any weight change. Those hormonal downstream effects move faster than body composition.
The weight normalisation comes later, and it comes indirectly: lower insulin → reduced cravings → less reactive hunger → less fat storage signal. You can see why tracking the scale won't capture this. The scale is at the end of a long chain of events. The earlier parts of that chain — the cravings, the energy, the cycle changes — move first.
The 8–12 week minimum timeline isn't a myth. It takes that long for the liver's glucose output to recalibrate, for peripheral insulin sensitivity to meaningfully improve, and for the downstream hormonal effects to accumulate. If you're at week six and nothing feels different, you're probably still in the early phase — not the failure phase.
The 5 Signals That Tell You Metformin Is Working
These are the markers that shift before the scale does. Track them consistently for 8–12 weeks and you'll have a real picture of whether your metformin is doing its job — one your GP appointment won't give you.
1. Fasting cravings
Pay attention to your hunger in the first hour after waking. If you're waking up ravenous for carbohydrates — a particular kind of urgent, insistent hunger that feels less like appetite and more like something your body is demanding — that's a sign your insulin is still spiking overnight. It's your liver doing its overnight glucose release, your insulin responding, and then glucose falling, triggering the craving response before you've even had breakfast.
As metformin reduces hepatic glucose output, this morning pattern tends to soften. Not overnight — gradually, over weeks. The first morning you notice you could take or leave the toast is the first data point. Track your morning craving intensity on a 1–5 scale at check-in. Over eight weeks, a genuine downward trend means the hepatic mechanism is responding.
2. Post-meal energy
The 90-minute energy crash after a carb-heavy meal is a classic insulin resistance signature. Insulin spikes hard, glucose is cleared rapidly, blood sugar drops below baseline, and you hit a wall. It's particularly pronounced in PCOS/PMOS bodies because the insulin response to carbohydrates is dysregulated in both size and duration.
As metformin improves peripheral insulin sensitivity, this crash tends to become less severe. The glucose spike after the same meal is lower, the drop is shallower, and the crash either doesn't come or hits less hard. Track your energy at 90 minutes post-meal on days you eat a carb-heavy lunch — relative to what you ate. If the post-meal pattern is softening over four to six weeks, that's the peripheral insulin sensitivity improving.
3. Cycle regularity
This is one of the most significant and most underrated signals. Metformin is one of very few non-hormonal interventions that can genuinely restore ovulation in PCOS/PMOS — by addressing the insulin-androgen feedback loop that disrupts the LH surge needed for ovulation.
You don't need to go from 45-day cycles to 28-day cycles to call this a signal. If your cycles were 45 days and they become 40, that's movement. If they were completely unpredictable and they're now landing in a 38–44 day window consistently, that's pattern emergence. Track your cycle day every day, log your period start, and compare cycle lengths across three or four months. Gradual shortening or increased regularity — even modest — is a direct hormonal signal that the androgen loop is responding.
4. Appetite rhythm
This is distinct from total appetite — it's about when you're hungry. Insulin-driven hunger is erratic and high-urgency: it arrives suddenly, feels pressing, and doesn't respond well to delay. You're not gently hungry. You're urgently hungry, and it arrived out of nowhere, and you can't concentrate until you eat something.
As metformin works and insulin becomes more stable, hunger tends to become more predictable and less urgent. You get genuinely, normally hungry at mealtimes — rather than being ambushed by appetite at irregular intervals. Track whether your hunger feels random or scheduled. Over weeks, a shift from erratic urgency to predictable appetite is one of the clearest signals of improving insulin rhythm that there is.
5. Mood baseline
This one surprises people. Insulin dysregulation affects neurotransmitter signalling — specifically dopamine and serotonin pathways. Chronically high insulin creates an environment where these signals are blunted and dysregulated. Many women with PCOS/PMOS describe a baseline "flatness" or low-grade irritability that they've normalised because it's been present for so long they've stopped noticing it.
As insulin improves on metformin, many women report mood improvements before any physical changes. Not dramatic ones — just a lift in baseline. A sense of being slightly more even, slightly less on edge. Track your mood scores daily and look at them as four-week rolling averages. A gradual, consistent upward drift is significant. It often shows up before cravings change, before cycles improve, before anything else.
What Your GP Looks For vs. What You Should Be Tracking
Your GP will check fasting glucose and HbA1c at your 12-week review. These are important, but they're 3-month averages — they don't capture the day-to-day insulin picture at all, and they can look perfectly normal while insulin resistance is still significant.
Fasting insulin is the more informative marker. It's not always included in a standard PCOS/PMOS blood panel, but it's worth requesting specifically at your 12-week review. Fasting insulin directly measures what metformin is targeting, and it gives you a much clearer picture of whether the hepatic mechanism is responding. HOMA-IR (calculated from fasting insulin and fasting glucose together) is even more informative if your GP is willing to run both.
But here's the gap that matters: even if both of those numbers look good, you can still feel terrible. Blood tests are point-in-time snapshots. They show what your insulin looked like on a Tuesday morning after a quiet weekend and eight hours of sleep. They don't show what your insulin does during a stressful week, or in the luteal phase, or after a run of poor sleep.
That's exactly where daily pattern tracking lives. Your GP sees you for 10 minutes every three months. Atlas sees you every day.
The gap between "your blood test looks fine" and "I still feel terrible most of the time" is real, it's common in PCOS/PMOS, and it's where your own tracking data becomes genuinely clinical. If you can show your GP that your craving scores have dropped from an average of 4.1 to 2.8 over eight weeks, or that your cycle length has shortened from 45 days to 38 — that's data a blood test won't capture, and it matters for your ongoing conversation about whether the dose is right, whether the timing should change, and what comes next. If you want to know what data makes the most impact in a GP appointment, the PCOS/PMOS GP appointment guide covers exactly what to bring and how to present it.
What It Means If It's Not Working After 12 Weeks
Some women don't respond to metformin. The estimate varies, but non-response affects roughly 20–30% of women with PCOS/PMOS who try it.
Non-response is more common in specific situations: very high baseline insulin levels, untreated thyroid dysfunction (which frequently coexists with PCOS/PMOS and significantly affects insulin sensitivity), chronically elevated cortisol load from ongoing stress, and poor sleep. If any of those factors are present and unaddressed, metformin has a harder job to do.
This is why tracking matters even when metformin isn't working. If you've tracked consistently for 12 weeks and none of the five signals above have shifted — cravings are the same, post-meal energy hasn't improved, cycles haven't moved toward regularity, appetite is still erratic and urgent, mood is unchanged — that's not a vague impression. That's actionable data.
Walking into your GP appointment and saying "I've been on metformin for 12 weeks and I still feel terrible" opens one kind of conversation. Walking in with 12 weeks of craving scores, cycle length data, energy patterns, and mood trends — all showing no change — opens a completely different one. It shifts the question from "does it feel like it's working?" to "here's the evidence that it isn't, and here's what I'd like to try next."
For women whose PCOS/PMOS is driven predominantly by insulin resistance and metformin hasn't worked, GLP-1 medications like Mounjaro (tirzepatide) work on a different pathway — targeting both GIP and GLP-1 receptors rather than purely hepatic glucose output. They're often more effective when metformin has failed, precisely because they address insulin resistance more directly and at a different point in the signalling chain. The Mounjaro and PCOS/PMOS post covers what to track alongside it and why the timeline is similarly non-linear. A weight loss plateau that isn't breaking despite doing everything right is often the data point that prompts the conversation about what comes next.
Start Tracking the 5 Signals Today
If you're on metformin and you don't know whether it's working, the answer isn't to wait and see. It's to start watching the right signals — specifically and consistently.
Atlas's daily check-in is built for exactly this. Morning craving intensity. Post-meal energy. Mood baseline. Cycle day. Food responses. Log these consistently for 8 weeks and you'll have a picture of your metformin response that no blood test and no quarterly appointment can give you.
You started metformin for a reason. You deserve to know whether it's working — not just hope it is, not just assume it isn't, but actually know. That's what the data gives you.
See Atlas plans → — 30 seconds a day, and within 4–8 weeks you'll have a pattern picture of your metformin response your GP will find genuinely useful. Reframe your daily check-in as a monitoring tool, not a habit. You're not just tracking your mood. You're building the evidence.
The information in this article is for informational purposes only and is not a substitute for medical advice. If you have questions about your metformin dose, timing, or whether it's right for your situation, speak to your GP or prescribing clinician.