Bella is made up of six drugs that are all known for their ability to support weight loss. Bupropion is a norepinephrine reuptake inhibitor, and naltrexone is an opioid receptor antagonist. Bupropion and naltrexone work together in the hypothalamus to reduce cravings and hunger. They activate POMC neurons in the hypothalamus, a brain region that produces a neurotransmitter that decreases the desire to eat. They also regulate feelings of pleasure in the mesolimbic area of the brain, reducing cravings to eat.

Oxytocin is a nine-amino acid peptide hormone made in the hypothalamus. In animal studies, administering oxytocin caused sustained weight loss by reducing food intake, increasing energy expenditure, and inducing fat breakdown. Oxytocin may also affect blood sugar control, a benefit independent of weight loss benefits. When oxytocin nasal spray was tested in humans, it led to similar effects: weight loss, decreased caloric intake, increased fat breakdown, and improved insulin sensitivity.

Vitamin B12 may help fight fatigue, boost energy, and support weight loss efforts. Vitamin B12 is a water-soluble vitamin that is involved in forming DNA and red blood cells. Research on how vitamin B12 affects metabolism is very limited. However, Vitamin B12 deficiency seems to be associated with an increased risk of obesity. In another study of over 9,000 people, having high levels of B12 was associated with a lower risk of obesity.

Topiramate is an anti-seizure medication for treating epilepsy and migraines that were found to have weight loss as a side effect. When tested in clinical trials, topiramate induced weight loss and improved blood sugar control in adults with type 2 diabetes and obesity. Some users report that topiramate alters their sense of taste, which may help with appetite control.

Metformin is used to control blood sugar in people with type 2 diabetes. Large studies have also demonstrated its weight loss potential. Metformin may modulate appetite control centers in the hypothalamus and alter the gut microbiome. The Diabetes Prevention Study showed that metformin decreased the risk of type 2 diabetes in at-risk patients by 31% over a three-year period. Average weight loss was about 4 pounds. That weight loss was sustained over a 10-year follow-up period. Weight loss strongly depended on adherence to the diet.