Dexcom G6


I'm not a doctor and this essay should not be taken as medical advice. It is an honest review by a type 1 diabetic, including decades of day-to-day with insulin pumps and years with Continuous Glucose Monitors (CGM). I've also worked in medical devices and digital health.

Dexcom G6

I got the Tandem t:slim X2 and Dexcom G6 on November 11, 2019, so in November 2022, I've spent 3 years with the device managing my day-to-day blood glucose.


The first insight for me when I got the X2:G6 combo was that it was tiresome to reach for the pump frequently just to check my blood glucose.

Getting the BG from the Dexcom G6 on my phone took more effort because I have a Google Pixel, which was not supported by Dexcom in 2019 and is sadly still not supported today. The ecosystem of smart phones and their app stores and software has remained a competitive disadvantage for Dexcom. Dexcom has made it clear from their dismal product support around smart phone apps that they simply do not understand the fact that the usability of their products is directly impacted by the mobile ecosystem 24x7x365.

Luckily, there's a very capable individual doing custom builds of the Android version of the Dexcom app on the internet. Just go through the form and you'll receive an APK build that can be loaded on an unsupported phone like my Pixel. It has worked perfectly for me for 3 years now. That person deserves kudos!

Once I realized that checking BG on my phone was going to be nearly as tiresome as on the insulin pump itself, I decided to check out watches, reflecting that blood glucose is arguably the killer app for digital watches, especially for someone who is highly active like me. I quickly realized that the Dexcom G6 supported the Apple Watch pretty well, but that wasn't an option for me having an Android phone.

I was also concerned about the cost of the Apple ecosystem having used it previously.

The real leap in learning came when I discovered an app on Github that runs on Fitbit Versa, Sense and similar devices. A quick trip to BestBuy and some configuration meant that I could track my BG on my wrist while exercising for a little over $100.

Glance has been a game changer for me since I use it daily when running or walking the dog and at-a-glance while sleeping has alerted me to problems that I otherwise would have missed. Kudos to Ryan Mason!

Once you get past the excellent Dexcom Clarity app, the most well-designed of the apps available is SugarMate. I use it everyday for information-rich spot checks.Sugarmate joins the list of quick exit diabetes startups acquired by either Dexcom or Tandem, like TypeZero.


Dexcom G6 sensors are expensive though that's started to change now that we have competition in the form of the Abbott Freestyle Libre 2.

G6 Sensors are over $300 per box of 3, each with a 10 day usage, with a membership and a prescription at Costco pharmacy.

This is the best pricing I've found without US health insurance.

There is competition in CGMs, but that competition is limited, given the proprietary integration with the insulin pump. This remains a sore spot in the ecosystem, even today.


I'm a big believer in evidence-based medicine. It's early but there's some interesting evidence available already. The easiest way to demonstrate the effectiveness of a medical device is 24x7x365 use for years with results. That population suvey is n of 1 or quantified self, and there's more to it than just the medical device (diet, exercise, and insulin); however, the medical device plays an outsized role in making good results possible, probable, and predictable, if not perfect.

The gold standard of results in diabetes control is Hemoglobin A1c. My HbA1c was 8.9 prior to acquiring the Tandem t:slim X2 and Dexcom G6 in the fall of 2019 and HbA1c tested in the same lab at 6.4 in February of 2020, and 6.0 in January of 2022 - both below the diagnostic threshold for type 1 diabetes, after only 3 months with the X2, G6, and Basal IQ.

I've found GMI to be conservative, meaning that GMI is generally higher than my lab's HbA1c - roughly .5 - 1.0 higher on average.

Regardless, the evidence speaks for itself. Prior to acquiring the X2 and G6, I had no way of approaching perfect control, where perfect control is defined as 100% in range for T1D which is is generally accepted as 70-180 mg/dl.

Today, I routinely have days where my blood sugar is 100% in control and most days are above the 70% in control benchmark, regardless of diet or exercise.


After using the G6 24x7x365 daily for 3 years, the one challenge that has emerged is that Dexcom G6 sensors are simply not reliable for me.

I'm thin and highly active having BMI < 20, training daily, completing a half marathon in 2021, and a full marathon in 2022. My endocrinologist points out that those characteristics present challenges for using subcutaneous adipose tissue as a proxy for plasma blood glucose since adipose tissue is not in abundance and these devices show poor data veracity without adequate adipose tissue, particularly in fasted states such as sleep and exercise. This is well-documented in the research literature.

I began seeing these issues with Dexcom G6 sensors in 2020 and the issues worsened in 2021 and have not gotten better in 2022 as my weight declined from 160 pounds to 140 pounds or less. However, at no time has my body fat measurement dropped below 10%.

The amount of time that I spent on the phone with Dexcom support was excessive and frequently at all hours of the night since the problem would present with alarms that cannot be disabled and are able to disable do-not-disturb mode on the smart phone and sound like an alarm system from the Austin Powers series.

That leaves the patient with two choices: tolerance (which is unrealistic at 3 AM) and powering the phone completely off, which silences it while having the side effect that alarms can't save the patient from potentially life-threatening hypoglycemia given that alarms emanating from the Tandem t:slim X2 alone are not sufficiently intense to wake me.

Dexcom has responded to this crisis by following the letter of the law: since I first reported the problem, they have replaced 2-3 dozen sensors under warranty while following the typical corporate communication playbook of not admitting design flaws or any legal culpability while not admitting the rather serious problem of the fact that, when the G6 is used in concert with a hybrid closed loop system such as the Tandem t:slim X2, inaccurate sensor readings on the low side have the potential to underdose the patient, and inaccurate sensor readings on the high side have the potential to overdose the patient.

This isn't just theory!

I've seen both of these scenarios playout while exercising and sleeping - two events that cannot be precluded, are frighteningly difficult to handle given failures in the aforementioned design of the alarm system, and no one at either Tandem or Dexcom seems to admit, document, or address which is distressing given that these are FDA-regulated devices in markets that aren't Therac 25 but have the potential to end badly in large populations.


I've tried to alleviate the problem by wearing two different CGM sensors concurrently. I wore an Abbott Freestyle Libre 2 from spring through fall 2022. That has done little to alleviate the problem since both sensors tend to move in parallel showing the same inaccurate readings in fasted states around sleep and exercise.