Though marijuana has been reported to stimulate appetite, we searched for a correlation between obesity and decreased marijuana use. We examined charts of all females referred for morbid obesity/weight management in a 12-month period. BMI and substance use data were collected from 297 charts. While 29% of the sample with BMI < 30 (n = 7) used marijuana in the past year, only 21% of those with BMI 30-39 (n = 84), 16% of those with BMI 40-49 (n = 110) and 14% (n = 96) of those with BMI > 50 used marijuana in the past year. Linear regression revealed a negative correlation between BMI group and percent marijuana use (R-squared = 0.96; P = 0.0173). These findings provide support for overeating as competition for drugs and alcohol in brain reward sites.