Tell whoever prescribes for you
Before the first capsule, not after the first month. It is the single habit that covers most of the risk described here, and it costs one sentence in an appointment you were having anyway.
The Aisle Where The Buyer Is Already Medicated
In most of the supplement shop, the worst case is that nothing happens. In this one aisle, the interesting case is that something does.
Quick answer
Blood sugar supplements are unusual because the people buying them are disproportionately likely to already take metformin, a sulfonylurea or insulin. That inverts the usual question. Instead of asking whether an ingredient does anything, the more useful question is what happens if it does, on top of a drug already doing it. The NIH warns that chromium may have an additive effect with antidiabetes medications and thus might increase the risk of hypoglycemia, and NCCIH advises anyone taking diabetes drugs to tell their health care provider about any herbal supplements.
The question everyone asks, and the better one
Stand in front of a shelf of supplements and the question that comes naturally is: does this do anything?
In most of the shop that is the right question, because the realistic worst case is that the answer is no and the money is wasted. A multivitamin that does nothing has cost you a multivitamin.
Move to the blood sugar shelf and the calculation changes, because of who is standing in front of it. Somebody shopping for a blood sugar supplement is far more likely than the general population to already be managing blood sugar — which for a great many people means a prescription.
So the better question becomes: what happens if it does do something, on top of a drug designed to do the same thing? That is a question about addition, and addition is where the risk in this aisle actually lives.
What the public health bodies actually say
The NIH Office of Dietary Supplements, on chromium: supplements “might have an additive effect with metformin or other antidiabetes medications and thus might increase the risk of hypoglycemia”. That is about as direct as these documents get.
NCCIH, in its guidance on diabetes and dietary supplements: “using herbal supplements such as cinnamon, St. John's wort, or aloe with conventional diabetes drugs can cause unwanted side effects”, and “people who take diabetes drugs should tell their health care providers about any herbal supplements they are taking”.
NCCIH again, on cinnamon: “it's unclear whether cinnamon supplementation is helpful for diabetes or weight loss”, and interactions between coumarin in cassia cinnamon and the liver have been reported.
Memorial Sloan Kettering, on berberine: repeated oral intake at doses used in some studies significantly decreased CYP2D6, 2C9 and 3A4 activity in human studies — the enzyme systems that clear a very large share of ordinary prescription medicines.
None of those is a warning about a brand. They are warnings about ingredients, and those ingredients turn up in most of the bottles on that shelf.
About the product behind this blog
Metaglucent is a once-daily capsule whose panel prints four amounts and hides thirteen more inside a single 528 mg Proprietary Blend. All four printed percentages are correct; none of the thirteen has a figure. We print the arithmetic the label leaves out.
Order NowRead the label firstWhy proprietary blends bite harder here
A proprietary blend removes the individual amounts. In most categories that is an annoyance for people who like to check things.
Here it removes the exact number a pharmacist would need. The question “how much berberine is in this?” has a right answer that matters, and the label does not contain it.
That is the sharp end of the blend problem, and it is rarely discussed. Blends are usually criticised as a way of hiding cheap formulation — a pinch of the expensive ingredient behind a wall of the cheap one. The stronger criticism in this aisle is that they remove information somebody clinical might have used.
Work out the ceilings anyway. Total divided by position. It will not tell you what is in there, but it will occasionally tell you what cannot be.
How this aisle differs from the rest of the shop
The same three questions, asked on four different shelves. Only one of them has the same answer every time.
| Multivitamins | Sleep | Joints | Blood sugar | |
|---|---|---|---|---|
| Is the buyer likely to be on a related prescription? | Rarely | Sometimes | Sometimes | Very often |
| Worst realistic case if it does nothing | Wasted money | Wasted money | Wasted money | Wasted money |
| Worst realistic case if it does something | Mild | Daytime drowsiness | Mild | Additive effect with a drug |
| Does the buyer have a number they can check? | Sometimes | No | No | Yes, and a clinician takes it |
| Is a proprietary blend a safety problem or an annoyance? | Annoyance | Annoyance | Annoyance | Closer to a safety problem |
The fourth column is the whole argument of this article. Every other shelf in the shop can be read with the ordinary question. This one cannot.
A category with a history
The FDA has for years published warnings about products marketed for diabetes and blood sugar found to contain undeclared pharmaceutical ingredients. In some cases those were the very prescription drugs a buyer might already have been taking.
That history is about a category and not about any particular bottle you are holding, and we are not implying anything about any product. We raise it because it explains why disclosure is worth more here than almost anywhere else in the shop.
It is also the practical argument for buying from a desk that can be telephoned. A named order desk, an order ID, a stated refund window and a return address are worth more than any badge, because none of the badges answer the phone.
And it is an argument for reading the panel rather than the front. A label that names a species, a plant part and a weight has told you something. One that names a mood has not.
Four rules for this aisle
Count the glucose-directed ingredients
If more than one or two ingredients on a panel have a blood sugar literature and you take medicine that does the same thing, the conversation stops being optional.
Do not stop or change a prescription
Nothing on a supplement shelf is a substitute for a medicine, and no supplement may lawfully claim to be. Changes to a prescription belong to the person who wrote it.
Learn what a low feels like
Shakiness, sweating, a racing heart, confusion, irritability or sudden hunger are commonly described signs of low blood sugar. That is a medical matter, and the response belongs with a clinician rather than a website.
Prefer amounts to adjectives
A panel with printed weights can be compared with research. A front panel with three inspiring words cannot be compared with anything.
Keep the receipt
A stated refund window is the only promise in this aisle that is genuinely enforceable, and it is worth knowing the date it expires.
Said plainly, about the product on this site
Metaglucent does not appear on any FDA warning list we are aware of, we have no basis whatever to suspect it of containing anything undeclared, and we are not suggesting it. Its seventeen ingredients are identifiable vitamin, mineral and plant material, and its panel is specific about species and plant parts. This article is about the aisle rather than the bottle, and it is on this site because a seller who left it out would be leaving out the most important thing a buyer in this category should know.
Base rates cut both ways
A category with a difficult history is a reason for more care, not for assuming the worst about every product on the shelf. Most bottles there are exactly what they say they are. The point of knowing a base rate is that it tells you how much checking is worth doing, and in this aisle the answer is more than in any other.
The most underused professional in this story
A pharmacist will check a supplement panel against your prescriptions, usually in a few minutes, usually without an appointment, and usually for nothing.
They are also the person most likely to recognise the specific problem in this category. An interaction that works through CYP2D6, 2C9 or 3A4 is bread-and-butter pharmacy, and berberine's effect on those enzymes is the sort of thing a pharmacist is far more likely to have front of mind than a busy general practice appointment.
The practical version: photograph the Supplement Facts panel before you buy, and show the photograph at the counter next time you collect a prescription. It costs one sentence and it is the highest-value minute available anywhere in this process.
If the answer is that a blend with no published amounts cannot be assessed, that is a useful answer too. It tells you the label, rather than the pharmacist, is the thing that failed.
This is not a reason to be frightened of the aisle
Most products on that shelf are exactly what their labels say they are, made in ordinary facilities by ordinary companies, and the great majority of people who take them come to no harm at all.
The point of knowing a category's history is not to assume the worst about every bottle in it. It is to know how much checking is worth doing before you buy, and in this aisle the answer is more than in any other.
More checking means three things, all of them cheap: read the panel rather than the front, tell whoever prescribes for you, and buy from somewhere with a telephone number and a refund window.
Do those three and most of what this article describes stops applying to you. That is a far more useful outcome than deciding the whole shelf is suspect.