Yohimbine is an alpha-2-receptor antagonist (a2-blocker), which causes your body to increase noradrenaline production. In effect, it is like other stimulants like caffeine in that it activates the sympathetic ‘fight-or-flight’ nervous system response and increases your energy expenditure, but yohimbine affects different receptors, which gives this a few unique properties.
For one, although yohimbine is a ‘natural’ supplement extracted from the yohimbine tree, it is not unconditionally safe. It is more of a wildcard than many other stimulants and it’s not to be screwed around with. At higher dosages, it has serious psychoactive effects ranging from impulsivity and increased sex drive to anxiety. It also comes with notable cardiovascular risk, including potentially elevated heart rate and blood pressure, especially when combined with other stimulants. Dosages upwards of 200 mg, around 10 times as much as used in research, can result in a coma, psychosis, retrograde amnesia, seizures, and tachycardia.
More sensible dosages are generally free from clinical side effects, but increased blood pressure and anxiety are often reported anecdotally and in studies.
Secondly, yohimbine’s fat burning effect is mainly noticeable during exercise and it is completely suppressed by the consumption of food. In practice this means yohimbine is likely only considerably effective when combined with intermittent fasting.