OBJECTIVE: The seed extracts from Nigella sativa is used by Unani physicians of traditional medicine (Hakims or Tabibs) and Ayurvedic practitioners (Vaids) in the treatment of several medical disorders including dyslipidemia, obesity, and hypertension. It is, therefore, important to prove or disprove the effectiveness, safety, and tolerability of powdered N. sativa (Kalonji) seed in capsules on serum lipid levels, blood sugar, blood pressure, and body weight in adults. DESIGN: The study design was a randomized, double-blind trial. SETTINGS/LOCATION: Conducted at Aga Khan University Hospital, Karachi, from February 2006 to January 2007. SUBJECTS: Half of the respondents received powdered N. sativa (Kalonji) seed in capsule and the rest received a placebo. INTERVENTION/OUTCOME: Baseline and after-intervention variables recorded were the following: body-mass index, waist-hip ratio, blood pressure, fasting blood sugar, serum lipids, serum alanine aminotransferase, and serum creatinine. RESULTS: One hundred and twenty-three (123) patients were recruited. Sixty-four (64) and 59 patients were randomized to the intervention and the control arms, respectively. Thirty-nine (39) patients in the intervention group and 34 in the control group completed the study. Favorable impact of powdered N. sativa (Kalonji) seed in capsule was noted on almost all variables, but results were not statistically significant because of small sample size. CONCLUSIONS: Favorable impact of powdered N. sativa (Kalonji) seed in capsule was noted on almost all variables, but results were not statistically significant. A larger study with adequate sample size is recommended.