Medtronic 780G

Last year, I got tired of waiting for Medtronic to get their act together and make nice with the FDA to get the 780G pump approved. So, I switched to a Tandem t:slim. Even though I had warranty coverage on my 770G through the end of 2024, Tandem/Dexcom were able to get insurance approval for the pump change.

So far, I have been quite happy with the results from the t:slim/Dexcom, with my A1C going from around 7.0 down to the 6.5 range. But, while I have have nothing but good things to say about the Dexcom, and am happy with many things on the t:slim, there are a few things really bug me with the t:slim … the biggest being the filling of the reservoir system is a joke and much more difficult than it needs to be; and the tremendous amount of insulin waste when changing cartridges.

But the biggest issue that I have is that the system is quite timid when it comes to auto-bolusing. Control-IQ does a pretty good job during normal days. But if you miss-count your carbs, or (for whatever reason) do not take a bolus prior to having a meal, it seems to take quite a while to get your BG back under control.

The 780 promises to be more aggressive in treating spiking BG levels. Auto-boluses can be given up to once every 5 minutes, as opposed to one an hour with the t:slim. Medtronic calls this “meal detection technology”. Also, after using the 670G and then the 770G for a long time, I know that the reservoir system, while a bit bulkier, is significantly simpler, and does not have any of the insulin waste as compared with the t:slim. (Tandem should really be ashamed at the design of the reservoir system of the t:slim. If Control-IQ didn’t work as well as it does, the reservoir system alone with have been enough for me to reject the t:slim.)

I know that many people had problems with Medtronic’s Guardian3 CGM, but I never did. Other than inaccuracies on the first day after a sensor change until the calibrations kicked in, it worked pretty well for me. So I am hopeful that the Guardian4 will be as trouble-free for me, with the benefits of (mostly) no calibrations. I do wish the 780 would work with the Dexcom, as the Dexcom G6 is much superior to the Guardian3 both functionally and aesthetically. But, other than the same aesthetics as the Guardian3 (which I don’t like at all), hopefully the functionality of the Guardian4 will be on-par with the Dexcom G6. And the next-gen Simplera from Medtronic looks to be even better … hopefully it will get approved more quickly.

I have registered for the 780 upgrade, and look forward to trying it out. I guess I am in a unique position in that I have plenty of supplies for the t:slim and Dexcom. So, once I get the 780 upgrade completed and receive new Guardian4 sensors, I can try one against the other side by side … I will be able to go back and forth to really see how they compare.

Should be interesting … we’ll see how it goes. I am really looking forward to getting started.


You have control over how much insulin you load.
I do a full fill, but I do a cartridge change when almost empty, and infusion set every 3-4 days. My cartridge fill us usually 4-5 days.

Did the same when using Medt, independent change schedule.


They created the cartridge just to make the pump smaller.
The mobi uses what looks like a syringe and you can see into it like the Medtronic pumps. Of course that only holds200 units, which works for me but not everyone.

You can make the x2 more aggressive by decreasing your carb factor.

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Agreed. Both the Medtronic and Tandem systems allow you to put any amount of insulin that you want to into the pump. And, both allow you to change your infusion set independent of the insulin cartridge.

All I was saying is that the t:slim makes that process ridiculously difficult … you have to insert a large needle into a very small white dot on the cartridge (and you can’t insert it anywhere within the white dot - you just have to guess where the magic spot is … most of the time, it takes multiple attempts); you suck out whatever air is in the bladder; you fill the syringe with however much insulin you require; re-insert the large needle back into that very small white dot (hopefully hitting that magic spot again, which almost always takes multiple attempts); then inject the insulin into the cartridge. For people like me that don’t have the best eyesight and have a slight hand tremble, it is not an easy process to perform.

With the Medtronic, you simply fill the syringe, attach the tubing, insert the syringe into the pump and you are done.

And, with the t:slim, when you change the cartridge/tubing, while you can go through the little white dot (again!!) to recover some of the remaining insulin in the bladder, without standing on your head and doing some unsanitary tricks, there is no way to recover any of the insulin in the tubing. I use the 43" infusion set, so that means that there is about 20 units of insulin that is unrecoverable every 3-4 days. That is a lot of insulin to waste. All of that can be easily recovered with the Medtronic infusion sets.

There is no comparison.

I do really like the size of the t:slim. I also like what Control-IQ has done for my control. But, if the 780 provides similar (or better) control, for me it will be a no-brainer.

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I absolutely love the form factor of the t:slim. I have no argument with the overall size/shape of the cartridge. It is the way they designed the fill process, and that none of the insulin in the tubing can be recovered when you change infusion sets … very poor.

Also love the size of the mobi, but I would be very reluctant to use a pump that required an external device to control it. I know that this is not true for all, but for me, while control from an app is great, my priority will always be to use a pump that can be controlled on the pump itself. The mobi requires an app on your phone to control. Too easy to be without the external device (your phone), so no control over the pump.

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Sorry you are having this issue. I wear 4x reading glasses when I fill and works fine. I close one eye, which helps get syringe lined up every time.

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What I dislike about the cartridge is thst I can’t see into it. I also think the pump rarely gets the units correct. I put in 100 units in and it tells me 70. And it doesn’t matter how much is in there , it will stop pumping when the counter reaches 0.
I think it wastes insulin in that regard. The actual changing the cartridge is no more easy or difficult than the Medtronic pumps.

The mobi will allow you to dose from the pump btw. You won’t be able to see the screen, but if you lost your phone you have a button to bolus and count the beeps to determine how much you want delivered.

Then you can also just download the ap into a new phone. You wouldn’t need to put up with no visibility for long.

I had my Animas pump, way back when,where the screen went blank and even though it was still operating, I couldn’t really use it and needed to go on injections till it was replaced.
That pump also developed cracks in the case on more than one pump.

So went on Medtronic for another 10 years. So now on Tslim, I still prefer it over MT but I keep my options open every 4 years for what looks like the best option.

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I am in a similar position. Switched to the Tandem-Dexcom combo mostly because of the Dexcom accuracy though. But still very tempted to go back on the 780 and the new Guardian 4 if CGM accuracy is comparable. While I have adapted to the ridiculous loading by now (+wasting of insulin and no “shoulder” once the pump says “0 units,” even though that’s not true), the fact that the 780 allows setting 100 as a target level is very appealing to me. (I run on 24/7 sleep mode with the Control IQ.) So I guess I am looking for real-world feedback from those of you getting the 780, with or without a switch from Tandem.

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With the used needle and a used cartridge from a t:slim cartridge change I made a “tool” to remove the insulin from the tubing.

My procedure is to use the new syringe/needle to extract any remaining insulin from the used cartridge. I then swap the needle for my “tool”, attach the used tubing and extract any remaining insulin. Swap back to the needle and extract the air from the new cartridge. Now fill the syringe with new insulin to the desired amount and fill the new cartridge.

@bsmorgan Wow … how creative. You should get some sort of T1D creative engineering award … that, or Tandem should offer you a job to design their infusion/cartridge systems. I am sure that your ideas would be so much more workable that what they have some up with so far! :wink:

@RLR56 I appreciate your perspective as I am in a similar predicament. I have a Medtronic 670G that I was very unhappy with for a variety of reasons and was ready to switch to Tandem and Dexcom as soon as my Warranty expired, however, that changed when my 670 started acting better (no idea why. It lets me sleep now and my TIR has improved) and I saw the 780G was coming soon. So……now I’m reconsidering my options. The 780G has been available in England for over a year, so I’m reading what the Brits who have actually used it are saying. I’m also comparing costs for each.

The things you mention, plus the costs, are my concerns with switching right now.

When do think you’ll make a decision? I’ll look forward to seeing your posts.

I’m in the same situation. My 770 (I paid the Pathway fee to upgrade from the 670) went out of warranty in September 2022. I waited until January and when there was still no news about the 780 I switched to Tandem/Dexcom. I never had a problem with the Guardian sensors. I had very few bad sensors over the 4+ years of using them and they always lasted a full week. I hated Auto Mode so I stayed in manual mode.

I started using the Tandem at the very end of February. My endo was no help with my settings. My manual mode Medtronic settings did not play well with CIQ, I was always going high. After several weeks I could see what CIQ was doing and made changes to my settings. I found I had to be very aggressive with them. I stay in Sleep Mode all day which means no auto corrections. My overnights are usually very good in sleep mode and during the day it’s easy enough to do a manual correction.

The cartridge fill is annoying but not as bad as I thought it would be. I do hate the insulin waste - so much waste!! I don’t like pulling the insulin out and adding it to fresh insulin. If you keep doing that you’re always going to have some really old stuff in the mix. I fill it completely and use it as long as I can. I don’t have a high TDD so it can last awhile. I change the set every 2-3 days, reusing the same cartridge & tubing. With Medtronic the only waste was pretty much what was in the tubing when my reservoir ran out. Maybe 10 units or so.

I like 90 degree plastic cannula sets. I used Silhouettes for 16 years, manually inserting in my abdomen, and ended up having so many “no delivery” alarms due to overusing the same areas. I switched to Mio Advanced and loved them. So easy to insert and I could use areas I could never reach before. The Autosoft 90/XC are pretty bad. Even when using SkinTac they pull out so easily. I was sent the 90s with my pump and just trying to disconnect them at the site could be a problem and required both hands. I switched to the XCs for my recent order and the connection is better but the inserter still sucks.

Before I started on Tandem my endo gave me a sample Dexcom. I wore it at the same time I wore the Guardian 3. While the graphs for both were the same - same peaks & valleys - the Dexcom always read higher. I’m hypo unaware so that made me nervous but the difference between the two sensors wasn’t so great that it would cause me to take that much extra insulin. I find that the Dexcom is far more unreliable after warmup. People say not to calibrate, or not to calibrate it during the first 24 hours, but I am not willing to deal with false numbers. It almost always reads high, as much as 100 mg/dl high, so I do calibrations in steps based off my meter. SOmetimes the difference between the meter & Dexcom is too much that if I put the meter BG in the calibration won’t take. If I do it in steps I can get it down to where it should be.

I am also looking forward to trying the 780 but if I feel Tandem/CIQ works better for me I will stick with it.

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Liz, I appreciate that perspective. I’m getting reports from the Brits that’s all over the place about M780. Some are ecstatic and others are exasperated. I can’t figure it out. I do know that Dexcom is not as perfect as it’s been portrayed for so long. I read plenty of issues about it in the diabetic community. Plus, I wore a Dexcom way back when I first got my M670. I had a couple of sensors left over and wore them on my arms at the same time and they were very close. I’ve never had sensor issues as long as the y a re on my upper arms. The y don’t work on my belly at all.

One concern I have is that since the M780 G is also a CGM that you don’t calibrate, how do you manage if it’s 100 points off from your finger stick? This would mean that I can’t go to sleep. Or, I’d have to set an alarm and get up to figure stick every hour.

I need auto mode. I don’t do well in manual mode, however, I want the option to go into Auto on certain occasions, like if I’m going to drink wine. I go low with alcohol and would need to back off my basal in anticipation of a fast drop. So, I’d need to half my basal for a few hours just to stay in safe range.

Honestly, I’m about to buy a new transmitter for my 670 G and keep moving along, since it’s behaving right now. The problem with that is that it’s out of warranty and if the pump conks out, I’m screwed. I can’t continue in that situation.

I have used a tandem pump for 7 years and currently have t:slim with control IQ. I have found that I can insert the needle anywhere into the white dot area to fill the cartridge or withdraw air and it works fine. The needle does not have to hit the magical spot where it inserts deeper. I can fill the cartridge easily each time this way and I do try to insert the amount of insulin I need to avoid waste. However, if I instill too much insulin, I then adjust and change my site on schedule, but continue with the same cartridge longer if there is still a lot of insulin remaining.

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My Tandem trainer (several years ago) told me to put a small amount of insulin in the syringe before pulling the air out of the bladder then let go of the plunger, let the plunger snap back and the cartridge would pull in insulin rather than air.
I’m curious if others were taught that step and if it’s really necessary. It seems like you could just pull out air and then not let the plunger snap back.
The pulling out and snapping back creates bubbles in that little bit of insulin in the syringe that you then have to tap out.

I just looked at the most recent manual. They changed the fill instructions at some point since I started, and it really is this awkward “eject the bubble into the air” method people talk about.

I’ve never done it that way. That’s wasn’t the way 6 years ago. I stick the full syringe in the port, and pull back on the plunger. Most of the bubbles rise up to the plunger, but a few good flicks gets all the air up there, including the little champagne bubbles. And I leave the big bubble up there, never pulling the syringe out to eject the bubble and then stabbing the port a second time. I just inject the insulin into the cartridge watching the needle, and stop pushing when the air gets into the dead space of the needle. You can see the air bubble through the transparent needle, so it’s really easy. This works out really well to avoid insulin waste, too. There’s a lot of wasted space in that luer lock connection between the syringe and needle (supposedly why Tandem switched to the smaller T:lock connection on the tubing, to avoid insulin waste… But I call BS on that). That air bubble just happens to perfectly fill the dead space, so you can get all the insulin out and you’re not chucking it in the trash. It’s a pretty gentle process, no violent snapping.


You can still calibrate the sensor on the 780g. In fact, if you do any meter tests and enter the number into the pump it will use it as a calibration.

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@Liz , that’s good to know. Thank you.

Can you share where you are gathering info from Brits who already have access to the 780 system? Would very much like to read such real-life experiences myself.

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Well, it has been a month since I registered for the 780 upgrade and have yet to hear anything from Medtronic. They said that they would be starting in mid-June (I believe), but so far it has been radio silence.

Has anyone else that has registered for the upgrade heard anything more from Medtronic?

@Dessito … I too would like to hear about experiences in Europe. I have poked around a little bit, and haven’t found a huge amount of real-life reviews out there.

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