Some thermogenic, or stimulant, herbal supplements are safe and effective, while others are not, according to About.com. Cayenne, green tea and seaweed are some of the safe herbal supplements.
Cayenne contains capsaicin, a component that stimulates saliva, digestion and metabolism. Green tea is a natural stimulant that is similar to coffee but with added vitamins and flavonoids. Seaweed helps stimulate the thyroid and is a good source of calcium and iodine, explains About.com.
Thermogenic supplements to avoid include herbal laxatives and ephedra, or ma huang. Herbal laxatives have the potential to prevent the bowels from working properly without stimulation, while high doses of ephedra raise blood pressure, increase heart rate and overstimulate the nervous system, notes About.com.