Test tube research showed that raspberry ketones cause hormonal changes that may be related to weight loss. This research is very preliminary, however, has been done only with mice. There are no studies that bear on the utility of so-called “exogenous” ketones in human dieting.
Raspberry ketones are on the FDA’s GRAS list (generally recognized as safe), but for cosmetic applications. Weight loss claims are unverified. In addition, the supplements sold as raspberry ketones are always synthetic. Natural ketones are indeed found in raspberries, but in very low concentrations. As I’ve said before, synthetic products may or may not contain the “active principle” that you’re looking for. In addition, they’re unregulated, so you may or may not get what you’ve paid for. Tests by Consumer Labs and other independent authorities have shown over and over that supplements frequently do not reflect the label claims with regard to concentrations or even contents.
If you’re interested in ketones, consider the ketogenic diet. Remember to consult your healthcare provider before launching, and be aware that this is not a lifelong regime. It has side effects and is definitely unsuitable for many common health conditions.