If you stop taking metformin, your blood sugar will likely rise back toward pre-treatment levels, and you may regain weight you lost while on the medication. How quickly and dramatically these changes happen depends on why you were taking metformin, how long you were on it, and whether you’ve made lasting lifestyle changes. Stopping abruptly isn’t dangerous in the way that stopping some medications can be, but the benefits don’t linger once the drug leaves your system.
Blood Sugar Rises Without a Safety Net
Metformin works by reducing the amount of sugar your liver releases and by helping your cells respond better to insulin. These effects wear off within a couple of days after your last dose, since metformin has a relatively short half-life and doesn’t build up in your body over weeks the way some drugs do. Once it clears, your liver goes back to producing more glucose than your body can handle, and your cells become less responsive to insulin again.
For most people with type 2 diabetes, this means a noticeable jump in fasting blood sugar within the first week or two. Over the following months, your HbA1c (the measure of average blood sugar over roughly three months) will climb as well. The size of the increase varies. Someone with mild insulin resistance who has also lost weight and changed their diet may see only a modest rise. Someone who was relying heavily on metformin to manage their numbers will likely see a sharper jump. A study published in Diabetes Spectrum found that when patients had their metformin discontinued and were switched to other oral medications, glycemic control often worsened, and many required additional drugs to compensate.
Weight Regain Is Common
Metformin modestly suppresses appetite and may reduce how much fat your body stores. When you stop taking it, that effect disappears. In a randomized trial, patients whose metformin was discontinued gained an average of 1.8 kilograms (about 4 pounds) during the first year and another 1.8 kg over the next three years. That’s a slow, steady creep rather than a sudden change.
The picture looks worse when metformin is replaced with certain other diabetes medications. Patients switched to alternatives gained an average of 3.8 kg (roughly 8.4 pounds), partly because some replacement drugs actively promote weight gain. If you stop metformin without starting another medication, the regain tends to be more modest, but it still trends upward for most people. The weight changes are gradual enough that you might not notice them week to week, which makes regular weigh-ins useful if you’re monitoring the transition.
What Happens for People With PCOS
Metformin is widely prescribed for polycystic ovary syndrome because it lowers insulin levels, which in turn reduces the excess androgens (male hormones) that drive symptoms like irregular periods, acne, and unwanted hair growth. Stopping it can reverse those improvements, but the timeline depends on how long you were taking it.
A study following 44 women with PCOS for six months after stopping metformin found that women who had been on it long-term (more than a year) experienced a significant drop in menstrual frequency. They went from having regular monthly periods back to missing cycles. Their levels of androstenedione, a precursor to testosterone, showed a borderline increase as well. Women who had only been on metformin short-term (under a year) fared better, with menstrual frequency staying relatively stable after discontinuation.
Five of the 44 women developed noticeably irregular cycles during the six-month follow-up and requested to restart metformin immediately after completing the study. The takeaway: the longer metformin has been managing your PCOS symptoms, the more likely those symptoms are to return once you stop.
Cardiovascular Effects Are Less Clear
Metformin has a reputation for protecting the heart, based partly on older landmark trials showing fewer heart attacks and strokes in people taking it compared to other diabetes treatments. The question of what happens to that protection when you stop is harder to answer. No large trial has directly measured cardiovascular event rates in people who discontinued metformin versus those who stayed on it.
What researchers do know is that the cardiovascular benefits are closely tied to better blood sugar control, lower insulin levels, and reduced inflammation, all of which metformin helps maintain. When those markers worsen after stopping the drug, it’s reasonable to expect that long-term cardiovascular risk rises too. Some experts have raised concerns that even temporary interruptions of metformin (for example, around medical procedures) carry risk if the medication isn’t promptly restarted, since gaps in treatment can lead to lasting deterioration in blood sugar management.
Withdrawal Symptoms and Safety
Metformin does not cause physical dependence, so you won’t experience withdrawal symptoms like you might with certain blood pressure medications or antidepressants. There’s no rebound effect where your blood sugar spikes dramatically higher than it was before you ever started the drug. The change is more of a return to baseline: your body gradually goes back to how it was functioning before treatment.
That said, “returning to baseline” can feel like a significant setback if metformin was doing a lot of the heavy lifting. Symptoms of high blood sugar, like increased thirst, frequent urination, fatigue, and blurred vision, can return over weeks. Some people don’t notice these symptoms because they developed gradually the first time around, so monitoring your blood sugar at home gives you a more objective picture than relying on how you feel.
When Stopping Might Be Appropriate
There are legitimate reasons to stop metformin. Some people achieve enough blood sugar control through weight loss and dietary changes that medication is no longer necessary. Others develop side effects like persistent gastrointestinal problems that don’t resolve even with extended-release formulations. Kidney function decline can also make metformin unsafe at certain thresholds.
If you’re considering stopping because you feel fine, it’s worth remembering that metformin treats a condition you can’t feel most of the time. Normal blood sugar readings while on the drug are evidence that the drug is working, not that you no longer need it. The most reliable way to know whether you can safely stop is to have your doctor check your HbA1c and fasting glucose, then make a plan for monitoring those numbers over the following months if you do discontinue.
People who stop metformin after significant lifestyle changes (losing 10% or more of their body weight, maintaining a consistent exercise routine, following a lower-carbohydrate diet) tend to have the best outcomes. Even then, regular blood work in the first year off the medication helps catch any creeping changes before they become a problem.