There generally tends to be a bit of common misconception around this question. The short answer is not really, but Studies have shown that the active compound found in chilli peppers, capsaicin, could well be effective in helping people lose weight.
As a result capsaicin does make it’s way into a lot of weight loss aids, but you’d have to eat an awful lot of chillis to make a dent.
Most chillies only contain around 0.025% capsaicin,  and you need 200mg of it for it to have any effect on weight loss according to most studies.
That means you’d need to eat a little under 2lbs or around a kilo of chillies to get enough capsaicin to have an effect. Particularly strong chillies could be more effective, but it’s still not realistic.
So What About Capsaicin?
Capsaicin in theory can slightly raise a persons metabolism, the general consensus is that it can make a difference of around 50-100 calories a day depending on if you’re exercising, because it effects body temperature it also seems to work better if you work out. At least that's the main way in which it functions, although it does have a couple of other benefits for weight loss.
To put it scientifically the mechanism involves the activation of Transient Receptor Potential Cation Channel (specifically TRPV1). Upon activation, capsaicin increases movement between cells of calcium and triggers your nervous systems response, resulting in increased energy expenditure through heat, otherwise known as thermogenesis.
Capsaicin also directly affects fat metabolism and energy balance. It stimulates Brown Adipose Tissue, a type of fat that burns calories to generate heat. By activating this tissue, capsaicin increases fat breakdown for energy.
Lastly, capsaicin contributes to weight management by improving insulin control. Proper insulin regulation is crucial for maintaining a healthy weight and preventing metabolic disorders. This gives it an added benefit for obese people as they are likely to have damaged metabolisms as a result of being obese.
Are There A Lot Of Studies To Back Up Chilli Extract For Weight Loss?
Yes, there have been several meta analysis [2,3,4] that reviewed multiple studies, which have shown that chillis can in fact aid weight loss in both overweight, obese and healthy individuals looking to simply lose a couple of pounds.
Interestingly a few studies have shown that it works better when combined with other ingredients, such as ginger  and it can be better absorbed with a black pepper extract such as bioperine which is often used to help the body absorb nutritional supplements.
Does Capsaicin Do Anything Else?
Capsaicin Side Effects
As you'd expect the side effects are similar to those of chillies, the most common of which is nausea and stomach issues. Allergies are of course possible and if the capsule containing it leaks the most common side effect of capsaicin is a burning sensation.
1 - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6264681/
2 - Wensen, Zhang., Qiang, Zhang., Lianke, Wang., Pan, pan, Wang., Ying, Qing., Changqing, Sun. (2023). The effects of capsaicin intake on weight loss among overweight and obese subjects: A systematic review and meta-analysis of randomized controlled trials.. British Journal of Nutrition, doi: 10.1017/S0007114523000697
3 - Mathias, Rollot. (2023). The effects of capsaicin intake on weight loss among overweight and obese subjects: A systematic review and meta-analysis of randomized controlled trials. British Journal of Nutrition, doi: 10.1017/s0007114523000697
4 - Cemre, Elmas., Ceren, Gezer. (2021). Capsaicin and Its Effects on Body Weight.. Journal of The American College of Nutrition, doi: 10.1080/07315724.2021.1962771
5 - Mohsen, Taghizadeh., Narjes, Farzin., Sara, Taheri., Mahnaz, Mahlouji., Hossein, Akbari., Fatemeh, Karamali., Zatollah, Asemi. (2017). The Effect of Dietary Supplements Containing Green Tea, Capsaicin and Ginger Extracts on Weight Loss and Metabolic Profiles in Overweight Women: A Randomized Double-Blind Placebo-Controlled Clinical Trial. Annals of Nutrition and Metabolism, doi: 10.1159/000471889