The short answer
Possibly. In a placebo-controlled trial published in 1996, people with type 2 diabetes who ate holy basil leaves had fasting blood sugar about 21 mg/dL lower than when they ate placebo leaves. Tulsi and metformin both lower sugar, so together they could lower it further.
We found no study of tulsi taken with metformin, and the trial abstract does not say what medicines people were taking. The metformin label warns that low sugar is more likely when it is combined with insulin or sulfonylureas such as glimepiride. If you take metformin, tell your prescribing doctor before you start tulsi capsules or extracts, and ask whether you should check your sugar more often.
Metformin is sold in India as Glycomet and Glycomet SR, and with glimepiride as Glycomet-GP.
At a glance
| What was seen | How it may work | Direction | Evidence |
|---|---|---|---|
| Lower fasting and after-meal blood sugar with holy basil leaves[1] | Not established | Holy basil lowered sugar; its added effect with metformin was not tested | RCT |
| Combined sugar lowering with metformin[2][3] | Two sugar-lowering agents taken together | Sugar may fall further; not measured in people | Theoretical by mechanism |
No listing is not a clearance. A missing interaction here never means a combination is safe.
The evidence, study by study
Crossover trial in type 2 diabetes, 1996 RCT
People with type 2 diabetes took holy basil leaves and placebo leaves in turn, without knowing which was which. Fasting blood sugar was 21 mg/dL lower and after-meal sugar 15.8 mg/dL lower with holy basil. The abstract does not give the number of people, the amount of leaf, how long each phase lasted, or what diabetes medicines they took.[1]
What your doctor may watch for
- Your blood sugar, and signs that it is running low, especially if you also take insulin or a sulfonylurea.[3]
What to tell your prescribing doctor
You can read this out, or show them this page:
“I am taking, or planning to take, tulsi (tea, leaves, capsules or extract, and how much) along with metformin. A trial found holy basil leaves can lower blood sugar. Should I check my sugar more often, and what reading should make me call you?”
Withheld until review
Questions people ask
Is tulsi good for diabetic patients?
One 1996 trial found that holy basil leaves lowered blood sugar in people with type 2 diabetes. It is a single trial that reported few details, and it does not replace diabetes medicine.[1]
Is tulsi tea different from tulsi capsules?
Possibly. The trial used leaves, and we found no study comparing tea, leaves and concentrated extracts. Their effect on blood sugar may not be the same, so tell your doctor exactly which form you use.[1]
Related
Type 2 diabetes (sugar): what Ayurveda offers
Some herbs, such as methi and karela, lowered HbA1c a little in trials. Taken with diabetes medicines, they can add to the risk of low sugar.
InteractionKarela (bitter gourd) and diabetes medicines
Added to metformin and dapagliflozin, a karela extract lowered HbA1c further in a 2026 study. With insulin or sulfonylureas, low sugar is the worry.
InteractionTurmeric and diabetes medicines (metformin, glimepiride)
Two curcumin trials point different ways: more benefit with metformin in PCOS, no added effect with glimepiride in diabetes. Neither counted low sugars.
InteractionTulsi and blood thinners like warfarin
A man on warfarin had a high INR after a herbal kadha that included tulsi. Tulsi's own role is not clear, and it has not been studied alone.
Sources
- Agrawal P, Rai V, Singh RB. Randomized placebo-controlled, single blind trial of holy basil leaves in patients with noninsulin-dependent diabetes mellitus. Int J Clin Pharmacol Ther. 1996;34(9):406-409. PMID 8880292.
- Merck Manual, Consumer Version. Holy Basil. Reviewed July 2025.
- Metformin hydrochloride tablets, US prescribing information (DailyMed).
Updated 4 November 2026
Taking tulsi with other medicines? A vaidya can check your full list.
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