01What did the 29-week US trial show on A1c?
A 29-week US program in obese type 2 diabetes put 141 people on metformin up to 2550 mg a day. Fasting plasma glucose fell 53 mg/dL from a 241.5 mg/dL baseline, against a 6.3 mg/dL rise on placebo in 145. Hemoglobin A1c at that same week 29 visit fell 1.4 points from 8.4, against a 0.4-point rise from 8.2 on placebo.
Week 29 is months, not a morning after the first 500 mg swallow. That trial is why this page talks about A1c on a months scale.
02If breakfast glucose is unchanged on day 3, is the tablet failing?
Day 3 is still inside the start. The 29-week A1c read was not a day-3 read. The dose may still be 500 mg twice daily, or even 500 mg once, while the gut is being watched. Home fasting numbers can move before A1c does. They can also sit still for a few mornings while the dose is still the opening 500 mg.
The metformin shelf opens at 500 mg. A later step, if glucose stays high and the gut allows it, is a weekly decision, not a day-3 emergency double.
03Does a missed swallow erase the next day's cover?
One missed tablet is a missed dose, not a reset of the weeks already taken. The next swallow is the next scheduled one. Doubling the morning tablet to 'catch up' is not a labelled make-up. A1c does not rewind because Tuesday's 500 mg sat in the bottle.
Immediate-release metformin is usually split across the day. Skipping both swallows on a busy day is two missed doses, still not a reason to take 1000 mg at once unless that was already the written line. Take the next meal-time tablet and leave the extra milligrams on the slip.
04How soon should labs come back after a start?
A1c is a months test. Checking it three days after the first 500 mg swallow does not read the 29-week effect. Fasting glucose at home can be watched sooner. The trial's A1c change sat at week 29, after titration up toward 2550 mg a day. Week 8 is still earlier than that visit.
EGFR is a different clock. Kidneys were supposed to be known before the start. The next kidney draw follows the clinician's plan, at least yearly, sooner if the person is older or already near 45. That kidney clock is not an onset clock.
05When do fasting glucose numbers usually start to move?
Home fasting numbers can drift down over the first days and weeks once a tolerated dose is in. That is a glucose read, not an A1c. Breakfast on day 2 is the wrong test of whether metformin 'worked.' A1c is a months test because it reads the last several weeks of glucose, not yesterday's swallow.
The labelled start is 500 mg twice daily or 850 mg once daily with meals. Some charts open at 500 mg once daily. The climb is weekly. A gut that is still settling on week one is not a failed tablet. The how-much page keeps that ladder.
06Why is the first week a titration week, not a verdict?
The label raises the daily total in 500 mg weekly steps, or by 850 mg every two weeks, based on glucose and on whether the gut holds. Judging the tablet before those steps is reading a start dose as a finished dose. The 29-week A1c read was taken after that climb, not before it.
Diarrhea and nausea are common in those first weeks. They are a reason to stay with meals and to wait on the next step, not a reason to call the first 500 mg a failure. An empty-stomach start makes that gut week louder.