Why 'fat burner' pills almost never work
The supplement industry sells dozens of products promising to speed up fat loss. Look closely at the ingredient list of most 'fat burners' and you'll usually find the main active compound is caffeine or a close relative, sometimes paired with green tea extract or L-carnitine.
Caffeine does modestly raise resting energy expenditure (thermogenesis) — but the effect is small, roughly 3–5% for a few hours, which works out to about one small apple's worth of calories. L-carnitine theoretically helps shuttle fatty acids into mitochondria for burning, but in people with normal carnitine levels (i.e. almost everyone), supplementing doesn't increase fat oxidation, because that transport step isn't actually the bottleneck.
The reality is that no legal supplement replaces a calorie deficit as the core driver of fat loss. At best, fat burners give a small, temporary boost to energy and focus — genuinely useful for a workout, maybe, but not magic in a bottle.