Prüvit Ketone Supplements are The World’s First and Only Pure Therapeutic Ketones Made Naturally. KETO//OS® NAT™ Puts Your Body Into Ketosis in 30 Minutes or Less. The Black Label Ketones has double the caffeine and double the ketones. For more information about the Black Label Ketones, check out this video. You can find all of the Ketones that are in inventory and ready to ship here.