Coleus amboinicus Lour (CA) has been used as a breast milk stimulant (a lactagogue) by Bataknese people in Indonesia for hundreds of years. However, the traditional use of CA is not well documented, and scientific evidence is limited to establish CA as a lactagogue. This investigation was conducted to elucidate the effect of traditional use of CA during the first month of lactation on quantity and quality of the breast milk. The results collected from the study show that CA supplementation increased breast milk production without compromising the nutritional quality of the breast milk. Lactating women receiving CA supplementation had a 65% increase in milk volume during the last two weeks of supplementation (from Day 14 to Day 28). This increase was greater than that of lactating women receiving Molocco+B12 tablets (10%) or Fenugreek seeds (20%). The residual effects of CA supplementation were seen even after the supplementation had ended for one month. Results of the present study confirmed the belief and the practice amongst the Bataknese people that CA can be used as a lactagogue in humans, and the use of CA might be suitable for lactating women in general.