The short answer
Not known in people. Karela may lower blood sugar modestly: in a four-week trial, 2,000 mg a day lowered fructosamine, a marker of average sugar, though less than metformin did. A Cochrane review found the trials too small and too varied to be sure of any benefit.
No human study has tested karela together with metformin, insulin or sulfonylureas such as glimepiride. Because both lower sugar, there is a theoretical risk of low blood sugar. If you take diabetes medicine and want to add karela juice or capsules, tell your doctor and ask whether you should check your sugar more often.
At a glance
| What was seen | How it may work | Direction | Evidence |
|---|---|---|---|
| Modest fall in fructosamine[1] | Glucose lowering; mechanism not settled | Adds to sugar-lowering drugs | RCT |
| Combined with glibenclamide in diabetic rats[3] | Changes in insulin signalling genes | Combined effect on sugar | Animal |
| Benefit uncertain overall[2] | - | - | Systematic review |
No listing is not a clearance. A missing interaction here never means a combination is safe.
The evidence, study by study
Trial against metformin, Thailand, 2011 RCT
People newly diagnosed with type 2 diabetes took bitter melon at 500, 1,000 or 2,000 mg a day, or metformin 1,000 mg a day, for four weeks. Only metformin and the 2,000 mg dose significantly lowered fructosamine, and bitter melon's effect was smaller.[1]
Cochrane review, 2012 Systematic review
Four randomised trials with 479 participants, mostly at high risk of bias, using a different preparation each time. There was no significant difference in sugar control compared with placebo. The reviewers did not pool the results.[2]
Rat study with glibenclamide, 2019 Animal
Diabetic rats were given bitter melon extract, glibenclamide (a sulfonylurea), or both for eight weeks, and blood sugar, insulin and HbA1c were measured. Animal results show the question is worth asking. They cannot tell us what happens in people.[3]
What to tell your prescribing doctor
You can read this out, or show them this page:
“I am taking, or planning to take, karela (juice, capsules or powder, how much) along with my diabetes medicine. Karela may lower blood sugar. Should I check my sugar more often, and what level should make me call you?”
Withheld until review
Related
Sources
- Fuangchan A, Sonthisombat P, Seubnukarn T, et al. Hypoglycemic effect of bitter melon compared with metformin in newly diagnosed type 2 diabetes patients. J Ethnopharmacol. 2011;134(2):422-8. PMID 21211558.
- Ooi CP, Yassin Z, Hamid TA. Momordica charantia for type 2 diabetes mellitus. Cochrane Database Syst Rev. 2012;(8):CD007845. PMID 22895968.
- Abdel-Rahman RF, Soliman GA, Saeedan AS, et al. Molecular and biochemical monitoring of the possible herb-drug interaction between Momordica charantia extract and glibenclamide in diabetic rats. Saudi Pharm J. 2019;27(6):803-816. PMID 31516323.
Awaiting review by The Good Vaidya Medical Board. Prepared from the sources below and checked against each one.
Published 4 November 2026 · Last updated 4 November 2026
On karela and other medicines? A vaidya can check your full list.
Medicine Check · ₹299