Context • Worldwide, 35 million people suffer from obesity. Mental disorders have been associated with being overweight or obese. Considerable evidence has shown a correlation between stress and the use of homeopathy and stress and obesity. However, few studies have examined the relationship between weight loss and homeopathic treatment of obesity. Objective • The study intended to evaluate the efficacy of a homeopathic treatment in preventing excessive weight gain during pregnancy in overweight or obese women who were suspected of having a common mental disorder. Design • The study was a randomized, controlled, double-blinded clinical trial. Setting • The study took place at the Center for the Social Support of Motherhood (São Paulo, Brazil). Participants • Participants were pregnant women who were enrolled at the center. Intervention • For the homeopathic group, 9 drugs were preselected, including (1) Pulsatilla nigricans, (2) Sepia succus, (3) Lycopodium clavatum, (4) sulphur, (5) Lachesis trigonocephalus, (6) Nux vomica, (7) Calcarea carbonica, (8) phosphorus; and (9) Conium maculatum. From those 9 drugs, 1 was prioritized for administration for each participant. After the first appointment, a reselection or selection of a new, more appropriate drug occurred, using the list of preselected drugs. The dosage was 6 drops orally 2 ×/d, in the morning and at night, on 4 consecutive days each wk, with an interval of 3 d between doses, up until the next appointment medical appointment. The control group received the equivalent placebo drug. Both groups also received a diet orientation. Outcome Measures • We evaluated pregnant women who were overweight or had class 1 or 2 obesity and were suspected of having a common mental disorder, with no concomitant diseases, in 2 groups: those receiving a placebo (control group, n = 72); and those receiving homeopathic treatment (homeopathy group, n = 62). Weight change during pregnancy was defined as the difference between the body mass index (BMI) at the initial evaluation and that recorded at the final evaluation, adjusted for 40 wk of gestation. In addition, the APGAR index in the newborn was evaluated as a possible complication. Results • The mean variation between baseline BMI and BMI at week 40 of gestation was +4.95 kg/m2 in the control group and +5.05 kg/m2 in the homeopathy group. The difference between the 2 groups was not significant (P = .815; 95% confidence interval [CI], -0.916 to 0.722). APGAR 10 at 5 min (59.6%in homeopathy group and 36.4% among control) was statistically significant (P = .016). Conclusions • Homeopathy does not appear to prevent excessive body mass gain in pregnant women who are overweight or obese and suspected of having a common mental disorder. Homeopathy did not change the APGAR score to modified clinical attention at delivery room. However, the evidence observed at APGAR 10 at minute 5 suggests that homeopathy had a modulating effect on the vitality of newborns, warranting further studies designed to investigate it.