Seeing a lot of posts about A1C dropping on Mounjaro and I get why people celebrate that number, it’s the one doctors actually put on your chart. But for PCOS specifically, I think fasting insulin is the more useful signal, and the two don’t always move in sync. My situation: started tirz 9 months ago. Fasting insulin was 22 at baseline (HOMA-IR around 5.1). A1C was 5.9, technically pre-diabetic but not alarming on paper. Classic PCOS insulin resistance picture where A1C looks “fine” but the underlying hyperinsulinemia is doing damage to cycles, androgens, skin. Nine months later, A1C is 5.2. Fasting insulin is now 9, HOMA-IR around 2.0. Cycles went from 45+ days to ~32. That hormonal downstream shift happened after insulin normalized, which tracks with the idea that androgen excess in PCOS is largely driven by hyperinsulinemia to begin with. The actual comparison: A1C reflects average glucose over ~3 months. Right metric for T2D management. For PCOS, it’s a lagging indicator and can look fine even when fasting insulin is 4x normal range. Fasting insulin / HOMA-IR reflects how hard your pancreas is working right now. This is the number that correlates with PCOS symptoms in my experience, including the cycle and skin stuff, not just glucose. People coming from a T2D context (7.5 A1C dropping to 6.2) are watching the right metric for their situation, that’s a meaningful improvement. But if you have PCOS and your A1C is borderline or low-normal, don’t assume insulin resistance isn’t a factor. The two can diverge significantly. Get fasting insulin with your next labs if you haven’t. Tirz moved both numbers for me, but insulin moved first and harder.
the case for fasting insulin as the primary PCOS metric is solid, and your numbers tell a genuinely compelling story. but “insulin moved first and harder” is doing a lot of work here - that’s a single n=1 timeline on tirz, which suppresses appetite and reduces hepatic glucose output simultaneously. hard to cleanly isolate which mechanism drove the insulin drop vs the A1C drop, and whether the sequence would hold for someone not on a GLP-1/GIP dual agonist. the cycle normalization piece is interesting but also confounds things - weight loss alone moves fasting insulin significantly, so attribution between the drug’s direct metabolic action and downstream effects of eating less is genuinely unclear. not disagreeing that fasting insulin is undertracked in PCOS. just wouldn’t generalize the sequencing from one 9-month tirz run.
The weight loss confound point is actually where I’d push back, bc it does the opposite of what iterate859 intends. They write “weight loss alone moves fasting insulin significantly” as if that undermines the sequencing claim, but if the mechanism is caloric restriction improving insulin sensitivity before glucose averages catch up, that’s precisely the argument for tracking fasting insulin over A1C in PCOS. Whether tirz moved my insulin through direct GIP action or through eating substantially less is genuinely hard to isolate, agreed. But the measurement sequence still holds either way. Fasting insulin is a faster, more sensitive signal than A1C regardless of which mechanism drove it down. The n=1 critique is fair and I won’t argue against it. But my original post wasn’t claiming tirz specifically causes this sequence in everyone. The broader point, that fasting insulin correlates more tightly with PCOS symptom burden than A1C does, has reasonable support in the endocrinology literature well before GLP-1s existed. Women with PCOS and entirely normal A1C but fasting insulin in the 20s are a documented and pretty common presentation. That’s not dependent on my 9-month run. It’s actually the reason some endocrinologists recommend fasting insulin at diagnosis rather than waiting for A1C to flag anything, because by the time A1C is elevated, the hyperinsulinemia has often been doing quiet damage for years.
the weight loss confound rebuttal actually lands, and I’d grant it more readily than my earlier reply implied. if the sequencing argument holds regardless of mechanism, that’s a more durable claim than I gave it credit for. the part I’d still push on is “fasting insulin correlates more tightly with PCOS symptom burden than A1C” as a general statement. the endocrinology support is real, but the correlation is noisy enough that fasting insulin alone probably shouldn’t be the only dial you’re watching. some of the PCOS literature showing insulin sensitivity improvement and symptom response also correlates with fasting insulin variability, not just absolute level. a fasting insulin of 9 after a low-protein dinner the night before reads differently than 9 after a consistent controlled intake window. the number is sensitive to a lot of variables that A1C isn’t, which cuts both ways. it’s a faster signal but also a noisier one. your specific trajectory (22 to 9, HOMA-IR 5.1 to 2.0, cycles regularizing after insulin normalized) is coherent and internally consistent. I’m not disputing the sequence you observed. the broader methodological point is just that fasting insulin’s sensitivity advantage and its noise problem are the same feature. worth knowing when you’re using it as a primary tracking metric, especially across multiple draws over time rather than a single snapshot.