Research synthesisHigh evidenceModerate effect6 studies · 5 beneficial · 1 neutral · 0 harmful
Across 6 studies, 5 reported beneficial effects of black cumin (Nigella sativa) supplementation on reducing hemoglobin A1c (HbA1c), with effect sizes predominantly moderate. The strongest evidence comes from a large 2025 meta-analysis (n=5026) showing significant improvement, while other meta-analyses report moderate-to-large reductions. Doses ranged from 200 to 4600 mg/day, and effects were observed primarily in populations with type 2 diabetes or metabolic syndrome; study durations were limited in reporting, but one study lasted 7 days.
- Effective dose range: 200 to 4600 mg/day
- Studied populations: type 2 diabetes patients, metabolic syndrome patients, adults
Caveats: Available evidence is overwhelmingly positive — clinical literature in this area is subject to publication bias (null-result studies are less likely to be published or indexed). The single neutral study had a small effect size and was not statistically significant, suggesting that benefit may not be universal. Most studies were meta-analyses of existing RCTs, not new trials; individual trial heterogeneity was high (I²=95.7% in one analysis). Duration data were sparse, making it unclear how long supplementation is needed to produce the observed effects.
Generated Jun 13, 2026