Monaz: Hello, I'm Monaz Mehta, editor in the Cochrane Editorial and Methods department. Obesity is a problem worldwide and several Cochrane Reviews examine interventions that might help to prevent or reduce it. These were added to in October 2019 with a new review examining the evidence on the drug fluoxetine. Here’s the lead author, Alejandro Gonzalez Garay from the National Institute of Paediatrics in Mexico City to let us know what they found.

Alejandro: In recent years, obesity has become a global public health problem. According to the World Health Organization, it affected approximately 650 million adults in 2016 and by 2030 the total number of obese people looks set to be more than 1.1 billion.
The reason for trying to reduce the problem is that obesity is a risk factor for numerous health problems, including heart disease, stroke, hypertension, diabetes, osteoarthritis, fatty liver, metabolic syndrome and respiratory disorders, as well as poor health-related quality of life. Therefore, we need effective strategies to reduce obesity and the costs of its complications.
Currently, a variety of pharmacological, non-pharmacological and surgical strategies are used to try to reduce weight and maintain weight loss. One of these is the drug, fluoxetine, which is one of the most commonly used medications in the treatment of depression. It is believed to affect weight control by changing a person’s appetite, resulting in lower food intake and normalization of unusual eating behaviors. However, it’s worth noting that the Federal Drugs Authority, or FDA, which regulates drugs in the USA, does not currently indicate its use for the treatment of obesity.
We did our review to find out what research studies say about fluoxetine’s effects and whether it could be used either alone, or in combination with other interventions, in adults who are overweight or obese. In the end, we found evidence that supports its use, but that it also has some important adverse events.
We included 19 randomized trials, involving just over 2200 overweight or obese adults without abnormal eating patterns in our review. They had been randomized mainly to fluoxetine at doses from 10 to 60 mg per day, or a placebo; with the intervention lasting from a few months to one year.  A few trials had also tested other therapies that might be anti-obesity agents, including omega-3 gel. 
The trials were from a range of countries: Brazil, Canada, China, Iraq, Ireland, Italy, the Netherlands, Spain, the United Kingdom and the USA, and were mainly focused on weight loss and adverse events. Some studies also reported data on body mass index and laboratory parameters, but there was too little data for us to do detailed analyses for these outcomes.
In general, we assessed the certainty of the evidence as low or very low, due to reporting bias and the small sizes of the trials. However, our findings show that fluoxetine produced a modest weight loss of about 2.7 kg by the end of the intervention period, compared with placebo when used at any dose, but especially when 60 mg a day is used. On the other hand, when compared to trial participants who did not take it, approximately twice as many of those taking fluoxetine experienced an adverse event, such as dizziness, drowsiness, fatigue, insomnia or nausea. 
Looking to the future, more high-certainty research is still needed into the effects of fluoxetine on its own, as well as into whether it is useful when combined with other anti-obesity agents and non-pharmacological interventions.

Monaz: If you would like to read the current version of the review, and watch for future updates if that new research is done, you can find the full review online. Just go to Cochrane Library dot com and search 'fluoxetine and obesity'.