Many people with diabetes or prediabetes try supplements to help control their blood sugar. However, some supplements can change how prescription diabetes drugs work—either by lowering blood sugar too much, or by affecting how much your body absorbs the drug.

1. Berberine

Berberine can add to metformin’s effects, meaning stronger glucose-lowering and gastrointestinal (GI) effects

Berberine (from plants such as Berberis) has blood sugar (glucose)-lowering effects and is sometimes used as a “natural” alternative to metformin.

Studies and reviews have shown similar mechanisms between berberine and metformin. For example, both can help reduce the amount of glucose produced by your liver. This can lead to additive or synergistic effects when taken together, so your blood sugar may drop too low. The similar effects also mean that GI side effects can be worsened.

Talk to your healthcare provider before planning to take berberine. If you are also taking metformin or another glucose-lowering medication, you may need to closely monitor your blood sugar levels and review your dosing with your provider.

2. Cinnamon

Cinnamon can increase the risk of low blood sugar when combined with medications.

Cinnamon and cinnamon extracts have been reported in multiple trials and reviews to modestly lower fasting glucose and hemoglobin A1c (average blood sugar level over two or three months) in some people.

This effect means that cinnamon supplements can enhance the glucose-lowering effect of prescription medications, such as sulfonylureas or insulin, especially when taken in concentrated form rather than as a sprinkle of the spice. 

Clinical evidence is mixed, but caution is warranted. “Natural” doesn’t mean harmless, and you should check your blood glucose more often if you start taking a cinnamon supplement.

3. Ginseng

Unpredictable effects mean ginseng may increase or decrease the effect of prescription diabetes medications.

Different ginseng preparations (e.g., American, Asian) and study designs produce inconsistent results, but studies show that ginseng can affect insulin secretion, glucose uptake, and postprandial (after a meal) glucose.

In individuals already taking oral blood sugar-lowering drugs or insulin, ginseng may have the potential to cause additive glucose-lowering effects, which can lead to hypoglycemia (too low blood sugar), or alter their responses to these medications.

Commercial ginseng products can vary widely in potency and formulation. Be sure to consult with your healthcare provider before starting this supplement.

4. St. John’s Wort

St. John’s wort may change drug metabolism, affecting how much of your diabetes medications get absorbed.

St. John’s wort increases the activity of CYP3A4 (a drug-metabolizing enzyme in the body) and certain drug transporters (proteins responsible for drug absorption, distribution, and elimination). As a result, it can reduce the blood levels of medications that share these pathways. For this reason, it is notorious for interacting with many different medications. 

While many diabetes drugs do not get broken down by the CYP3A4 enzyme, St. John’s wort has been shown to alter the way metformin works in your body in at least one trial. It can also interact with many other medications.

Because of its unpredictability with interactions, it’s recommended to avoid combining St. John’s wort with complex medication regimens without supervision from your healthcare provider.

5. Aloe Vera

Aloe vera can lower glucose and interact with diabetes medications.

Aloe vera has been studied for its effects on processes that contribute to high blood sugar levels. Studies suggest that it may be beneficial in reducing fasting glucose and hemoglobin A1c levels, particularly in stabilizing blood sugar levels after meals.

However, the extent to which aloe vera affects blood sugar levels is unknown. Tell your healthcare provider if you are taking an aloe vera supplement. Keep in mind that aloe vera formulations also vary, and some can cause side effects, such as GI upset.

6. Chromium

Chromium supplementation has shown modest improvements in insulin sensitivity and hemoglobin A1c in some studies. Other studies have shown benefit only in people with poor nutritional status or already low chromium levels. 

Because chromium can enhance insulin action, using it with a prescription blood sugar-lowering drug can raise the risk of hypoglycemia, especially if the doses are higher than those found in multivitamins.

According to the Food and Drug Administration (FDA) and the Institute of Medicine, it is safe when taken at a dose of 200 micrograms daily for up to six months.

Keep in mind, chromium supplements may also carry side effect risks like GI upset or headaches. Caution should be used if you have kidney or liver issues. Talk to your healthcare provider about whether chromium supplements may be beneficial for you.

The popularity of matcha continues to boom. But recent videos on social media have suggested it could be bad for you if you have low iron.

One Sydney woman recently told media she had “no idea” her daily matcha latte could affect her health until she started experiencing headaches, and noticed her hair and nails were brittle and she was bruising easily. Blood tests found she was severely low in iron.

Similar videos on TikTok show women in hospital getting iron transfusions — and blaming their matcha habit.

So, let’s unpack this. How healthy is matcha? And can it really cause low iron?

What is matcha?

Matcha is a fine powder made from dried and ground-up green tea (Camellia sinensis) leaves. It has recently gained popularity as a drink and a flavor variety in many different foods.

Matcha contains many beneficial compounds (for example, dietary fiber and polyphenols) as well as being a source of caffeine.

Including matcha, or green tea, as part of a balanced diet may provide health benefits such as supporting healthy brain function and blood pressure.

However despite its health benefits, research has shown that drinking a lot of green tea is linked to lower levels of iron in the blood.

We need iron – but can’t make it

Iron is an essential micronutrient that helps transport oxygen around the body, as well as supporting many other important biological processes.

Our bodies can’t make iron, so we need to get it from our diet to support these functions. But even if we eat a lot of iron-rich foods, other things in our diet — such as coffee, red wine, calcium-rich foods and yes, matcha — can interfere with absorbing the iron.

So people with low iron levels need to be careful.

In particular, women who menstruate have an increased risk of low iron because of iron lost through bleeding.

You may have an iron deficiency if your iron falls below certain levels – typically for adults, less than 30 micrograms of iron per liter of blood. There are different cutoffs for children.

Iron deficiency anemia is a condition where very low levels of iron affect the functioning of red blood cells. It is diagnosed based on levels of hemoglobin in the blood (these cutoffs vary by age, sex and pregnancy status).

What does matcha do to iron levels?

There are two main components in green tea that stop us absorbing iron. These are polyphenols and phytic acid (also known as phytate).

Both polyphenols and phytic acid have their own health benefits, for example, protecting against chronic diseases such as type 2 diabetes. But they also bind to iron and prevent it from being absorbed into the body.

So, if you have a lot of food or drink that contains these components — especially in combination with iron-rich foods — they can reduce iron absorption.

However, it’s not only matcha that can interfere. Phytic acids are also found in other teas and many plant foods, such as nuts, cereals and legumes. Tea, coffee, berries, and other fruits and vegetables are also high in polyphenols.

How much matcha will affect your iron levels?

This varies between people.

One study showed people who drink three or more cups of green tea a day had lower blood iron levels than those who drink less than one a day. But they didn’t experience iron deficiency any more often.

However other research has linked moderate green tea consumption (two cups a day) to iron deficiency anaemia.

Whether or not your matcha latte will contribute to an iron deficiency depends on many other factors, including your existing iron levels.

So, what about matcha-flavored foods?

In these — for example, matcha ice cream — the actual amount of green tea powder is very low. This means it’s unlikely to significantly affect iron absorption.

But it’s not just about quantity — when you drink your matcha also matters.

To reduce the impact on iron absorption, it’s recommended you have green tea separately from meals — at least one hour between eating and drinking tea.

What else to keep an eye on

Multiple other factors in your diet can influence iron absorption. What you eat may either exacerbate or counteract the effects of your matcha latte on iron absorption.

Overall, balance is key to ensure you are getting the full spectrum of nutrients the body requires.

To support iron levels, you can incorporate iron-rich foods (such as beans, lentils, meat, fish and fortified cereals) into a healthy diet.

Eating vitamin C-rich foods (such as capsicum, broccoli, kiwifruit and other fruit and vegetables) along with foods that contain iron can help to enhance iron absorption.

If you are concerned about your iron levels, you should speak to a health-care professional — especially if experiencing symptoms of iron deficiency (such as tiredness, weakness or dizziness).

A blood test can diagnose low iron levels. If you have an iron deficiency, your GP or dietitian will help you manage symptoms and work out what is right for you.

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