Cross-sectional observational studies are lower-quality studies that collect data at a single point in time. One such study associated cannabis with greater fat mass,  but the others associated it with a smaller waist,  lower BMI,   and lower prevalence of obesity.  Even a higher-quality prospective observational study found no association between extensive cannabis use and higher BMI. 
Two small, short RCTs have investigated THC as a treatment option for anorexia nervosa.  
Cannabis (aka marijuana) is a popular recreational drug that also has a variety of potential medicinal uses, from boosting appetite to reducing nausea and anxiety.  In cancer patients, cannabis may help ease the pain associated with chemotherapy while simultaneously increasing appetite (a serious side effect of chemotherapy being nausea). 
HIV-associated wasting syndrome
Yet in spite of these successes, rimonabant failed to earn approval from the U.S. Food and Drug Administration (FDA) and was withdrawn from the European market,  due to side effects that include nausea, dizziness, severe depression, and suicidal thoughts.  
Aside from euphoria, this increase in appetite is probably cannabis best-known effect — you might refer to it as “the munchies”. Historical sources indicate that people as early as 300 BCE knew that cannabis stimulated appetite, especially for sweet and savory food. 
People in the intervention groups received 2.5 mg of dronabinol twice daily for 4 weeks.
The limbic forebrain, where it may enhance food palatability.
To understand their answers to these questions, first, a quick tutorial. Cannabis plants contain more than 100 cannabinoids, although the therapeutic and psychoactive effects of most of them aren’t yet known. The two most-researched cannabinoids are CBD and tetrahydrocannabinol, or THC, the main psychoactive cannabinoid. THC makes you high; CBD doesn’t. And, it turns out, they affect appetite in different ways.
Second, THC hits a part of the brain that controls hunger. “The appetite-promoting effect of THC is mediated by CB1 receptors located in areas of the brain involved in appetite control,” explains George Kunos, scientific director at the National Institute on Alcohol Abuse and Alcoholism in the National Institutes of Health in Bethesda.
As a dietitian, I always receive an influx of New Year’s emails predicting upcoming food trends. This year, several experts have forecast an increase in foods and beverages containing cannabidiol, a chemical compound found in cannabis plants. More colloquially called CBD, cannabidiol has been approved by the Food and Drug Administration to treat some forms of epilepsy and shows potential in treating pain, nausea, anxiety and depression — without making users high.
THC produces the well-known cravings for sweet and fatty foods through several mechanisms, according to the experts I consulted. First, “THC increases the hormone ghrelin, which causes you to feel hungry,” says Janice Newell Bissex, a registered dietitian and holistic cannabis practitioner in Melrose, Mass. If your stomach is empty, she says, you produce more of the hunger hormone ghrelin, which tells the brain to generate the sensation of hunger. But THC can increase ghrelin and trigger the feeling of hunger even if your stomach isn’t empty.
But what about its effect on hunger? After all, smoking or ingesting cannabis is associated with the munchies. So, I wondered: Does CBD have the same effect? Could a trend toward CBD-infused foods lead to weight gain? And how might CBD affect people who have conditions that make it difficult to keep weight on (such as those with HIV/AIDS, cancer, eating disorders or depression)? I decided to consult some experts.
And third, THC boosts dopamine, the “feel-good” chemical in the brain, “so you get more pleasure from eating,” Bissex says. “THC can increase the sense of smell and taste, so people are more inclined to want to eat.”