For most healthy adults, wearing a CGM without diabetes isn’t worth it: the research so far hasn’t shown that it improves health, and normal readings already bounce around more than many people expect. It can make sense in a few situations, such as known prediabetes or when a doctor wants to look at a specific problem, but a cheap HbA1c or fasting glucose test answers the main question (do I have diabetes or prediabetes?) more reliably.
Continuous glucose monitors (CGMs) used to be prescription devices for people with diabetes. That changed in the US on 5 March 2024, when the FDA cleared the first over-the-counter CGM, the Stelo biosensor, for adults 18 and older who don’t use insulin. The FDA’s announcement specifically mentions people without diabetes who want to see how diet and exercise affect their blood sugar.
What a CGM measures and how it differs from a finger-prick test
A CGM is a small sensor with a thin filament that sits just under the skin, usually on the back of the upper arm. It doesn’t read blood. It reads glucose in the interstitial fluid, the fluid around your cells, and sends the numbers to a phone app or reader.
Because glucose reaches the blood first and then moves into that fluid, Cleveland Clinic notes that CGM readings can lag a few minutes behind a finger-prick test. Sensors typically last 7 to 15 days depending on the brand. The over-the-counter sensor cleared by the FDA is worn for up to 15 days and shows readings every 15 minutes.
If you want a refresher on why blood sugar rises and falls in the first place, our guide to how glucose fuels your body covers the basics.
What normal CGM readings look like in people without diabetes
The best reference data comes from a 2019 multicentre study in The Journal of Clinical Endocrinology & Metabolism. Researchers fitted 153 healthy, non-obese people aged 7 to 80 with blinded sensors (they couldn’t see their numbers) for up to 10 days. Here’s what they found:
| Measure | Healthy participants (median or mean) |
|---|---|
| Average glucose, most age groups | 98 to 99 mg/dL (5.4 to 5.5 mmol/L) |
| Average glucose, adults over 60 | 104 mg/dL (5.8 mmol/L) |
| Time between 70 and 140 mg/dL (3.9 to 7.8 mmol/L) | 96% of the day |
| Time above 140 mg/dL (7.8 mmol/L) | 2.1%, about 30 minutes a day |
| Time below 70 mg/dL (3.9 mmol/L) | 1.1%, about 15 minutes a day |
| Day-to-day swing (coefficient of variation) | 17% |
Two things stand out. First, healthy people do go above 140 mg/dL (7.8 mmol/L) for a short time most days, usually after meals. Second, most participants had at least some readings between 55 and 69 mg/dL (3.1 to 3.8 mmol/L). Readings below 54 mg/dL (3.0 mmol/L) were uncommon. So a brief dip into the 60s on your app isn’t automatically a sign of a problem, and neither is a post-meal peak.
Is a CGM without diabetes worth it? What studies show
The short answer from researchers is “not proven.” A 2024 narrative review in Diabetic Medicine looked at how CGMs are marketed to people not living with diabetes: to spot abnormal glucose early, to change behaviour, and to improve metabolic health. The authors found a lack of consistent, high-quality evidence for any of those uses. They pointed out that clinical guidelines don’t recommend CGMs outside type 1 diabetes or insulin-treated type 2 diabetes, and they called for commercial claims about usefulness in healthy people to be labelled as misleading.
Some earlier research did catch attention. A 2018 study in PLOS Biology found that people classed as normal by standard tests still reached glucose levels in the prediabetic range 15% of the time and the diabetic range 2% of the time on a CGM. What it doesn’t show is that those spikes harm healthy people, or that trying to flatten them improves long-term health. Other researchers later questioned the way that study grouped people into “glucotypes.”
In short, a CGM gives you plenty of data, but nobody yet knows what most of it means when your standard tests are normal.
Accuracy limits and false alarms
- Two sensors can disagree. In a 2020 study in The American Journal of Clinical Nutrition, 16 adults without diabetes wore two different brands of CGM at the same time across 760 meals. The two devices ranked which meals caused the biggest glucose rise quite differently. The authors concluded that using CGMs to personalise diets “may be premature.”
- Some medicines and supplements interfere. Acetaminophen (paracetamol), vitamin C and hydroxyurea can make some sensors read higher or lower than your true level, according to Cleveland Clinic.
- Readings lag. During exercise or right after a meal, the number on your phone may be a few minutes behind your blood.
- Lows may not be flagged. The FDA says the over-the-counter device is not for people with problematic low blood sugar, because it isn’t designed to alert you to it.
If a reading doesn’t match how you feel, check it with a finger-prick meter before you act on it. And the FDA’s advice is clear: don’t make medical decisions based on the device alone without talking to your doctor.
Who might benefit from a CGM
There are situations where wearing one, ideally with a clinician who can interpret it, has a clearer purpose:
- Prediabetes. If you already know your HbA1c or fasting glucose is in the prediabetes range, a short trial can make the effect of meals, sleep and activity visible, which some people find motivating. Cleveland Clinic lists prediabetes and obesity among the reasons a provider may suggest one.
- Unexplained symptoms. A doctor may use a CGM to look for patterns of low or high glucose if you have repeated shakiness, sweating or confusion that hasn’t been explained.
Pregnancy is a special case. If you’re at higher risk of gestational diabetes, for example if you’re over 40, have a BMI above 30, had gestational diabetes before or have a parent or sibling with diabetes, the standard approach is still an oral glucose tolerance test, usually between 24 and 28 weeks of pregnancy. Don’t swap that test for a consumer CGM unless your maternity team tells you to.
Small changes such as choosing higher-fibre carbohydrates or building up regular exercise, like a beginner running plan, help glucose control whether or not you’re wearing a sensor.
Risks: anxiety, food rules and skin problems
The physical risks are small. The FDA’s review of the over-the-counter sensor reported skin irritation, local infection, and pain or discomfort at the insertion site.
The bigger risk is what constant numbers do to your relationship with food. The authors of the Diabetic Medicine review warned that CGM use in healthy people could cause anxiety about what counts as normal, and could raise the risk of eating disorders such as orthorexia (an unhealthy fixation on “clean” eating). A spike after a bowl of porridge, a banana or a slice of wholegrain bread doesn’t make those foods unhealthy. If you notice yourself cutting out whole food groups, skipping meals to keep a flat line, or feeling stressed every time you check the app, take the sensor off and talk to your doctor.
Cheaper, proven alternatives: HbA1c and fasting glucose
If your real question is “am I heading towards diabetes?”, standard blood tests answer it. The NIH’s diabetes institute (NIDDK) uses these cut-offs:
| Test | Normal | Prediabetes | Diabetes |
|---|---|---|---|
| HbA1c | Below 5.7% | 5.7% to 6.4% | 6.5% or above |
| Fasting plasma glucose | 99 mg/dL (5.5 mmol/L) or below | 100 to 125 mg/dL (5.6 to 6.9 mmol/L) | 126 mg/dL (7.0 mmol/L) or above |
| Oral glucose tolerance test, 2 hours | 139 mg/dL (7.7 mmol/L) or below | 140 to 199 mg/dL (7.8 to 11.0 mmol/L) | 200 mg/dL (11.1 mmol/L) or above |
You don’t need to fast for an HbA1c test, because it reflects your average blood sugar over the past two to three months. Our comparison of HbA1c vs fasting blood sugar explains which test suits which situation. These tests have agreed diagnostic thresholds. A CGM worn by someone without diabetes doesn’t.
When to see a doctor
Whether or not you wear a sensor, see a doctor soon if you have:
- Feeling thirsty all the time, peeing more than usual, or losing weight without trying
- Constant tiredness, blurred vision, cuts that heal slowly, or repeated thrush
- Repeated episodes of shakiness, sweating, a racing heart or confusion, especially if they ease after eating
- CGM readings that stay above 140 mg/dL (7.8 mmol/L) for long periods, or a blood glucose reading of 200 mg/dL (11.1 mmol/L) or more with symptoms
- A blood test result in the prediabetes or diabetes range
Call your local emergency number or go to hospital straight away if you or someone else has symptoms of diabetic ketoacidosis: being very thirsty and peeing a lot together with stomach pain, nausea or vomiting, deep breathing, fruity-smelling breath, or drowsiness and confusion. This can happen in people who haven’t yet been diagnosed with diabetes, particularly children. Get emergency help too for anyone who has a seizure or can’t be woken. Don’t drive yourself.
For a full overview of the different types of diabetes and how they’re treated, see our guide Diabetes Explained.
Frequently asked questions
What should a CGM read if you don’t have diabetes?
In healthy adults, average glucose is usually around 98 to 104 mg/dL (5.4 to 5.8 mmol/L), with about 96% of the day spent between 70 and 140 mg/dL (3.9 and 7.8 mmol/L). Short rises after meals and brief dips into the 60s mg/dL are common.
Can a CGM detect prediabetes?
Not officially. Prediabetes is diagnosed with HbA1c, fasting glucose or an oral glucose tolerance test, which have agreed cut-offs. There are no accepted CGM criteria for diagnosing prediabetes in people without diabetes.
Are CGMs accurate for non-diabetics?
They’re reasonably good at showing overall patterns, but less reliable for fine detail. Two different sensors worn at the same time can disagree about which meals raise glucose most, and medicines like paracetamol or vitamin C can affect some readings.
Do you need a prescription for a CGM?
In the US, the FDA has cleared over-the-counter CGMs since 2024 for adults 18 and older who don’t use insulin. Rules differ between countries, so check with a local pharmacist or doctor.
Is a glucose spike after eating bad for healthy people?
A short rise after a meal is normal. There’s no good evidence yet that flattening every post-meal rise improves health in people whose standard blood tests are normal.
This article is for general information and is not a substitute for advice from a doctor. If you have symptoms or a health condition, please consult a qualified healthcare professional.
