This study aimed to analyze the effects of deficit
irrigation strategies on energy efficiency and the yield of Bacopa monnieri cultivated under a drip irrigation system at the Pharma-Agroforestry District, Rajamangala University of
Technology Lanna Nan. Five irrigation regimes were evaluated over a total cultivation period of 137 days: 0.5 L per plant per day, 1.0 L per plant per day, 1.0 L per plant every other day, 1.5 L per plant every other day, and 1.5 L per plant every three days. The study assessed plant growth performance, yield, energy efficiency, Energy Productivity Index (EPI), Specific Energy Consumption (SEC), and energy costs. The results indicated that appropriate selection of irrigation regimes can significantly improve production efficiency while reducing energy consumption and costs in Bacopa monnieri cultivation. The treatment of 1.5 L per plant every other day produced the highest yield (6.89 kg fresh weight and 1.0 kg dry weight), with statistical significance (p < 0.05). In terms of energy performance, the 0.5 L per plant per day and 1.5 L per plant every other day regimes exhibited the highest energy efficiency, with EPI values of 1.72–1.73 kg/kWh and the lowest SEC of 0.58 kWh/kg, resulting in the lowest energy costs of 3.06–3.07 THB/kg (fresh weight) and 22.66–22.69 THB/kg (dry weight).