Yohimbe Fuel
If ever possible, try to use pharmaceutical yohimbine rather than yohimbe bark. It's not just that you can clearly dose with pharmaceutical yohimbine. Yohimbe bark also contains a number of other alkaloids, apart from yohimbine, and these other alkaloids account for some of the possible irritating side effects, such as headaches.
Most of what you can buy as yohimbe capsules unfortunately seems to contain many of the other alkaloids but very little yohimbine.
For that reason, if you cannot get hold of pure pharmaceutical yohimbine, at least buy standardized yohimbe. A common yohimbe product that has been standardized is Twinlab's Yohimbe Fuel.
Each capsule of Yohimbe Fuel contains: Yohimbe Bark Extract 400 mg, with 8 mg of yohimbine, Calcium 40 mg, Phosphorous 32 mg.
Please note that it is comparatively easy to standardize yohimbe for a set amount of yohimbine because its exact molecular structure is known. Isolating yohimbine with reagents is relatively simple, and an industrial process for producing it has existed since the 19th century.
Isolating the active ingredients of other herbs, such as Tongkat Ali, butea superba, and kaempferia parviflora, is more complex. However, industrial processes do exist to standardize extracts for specific compounds, such as eurycomanone and methoxyflavones. While standardization for these herbs may be less universally regulated or historically established than pharmaceutical yohimbine, claims of standardization for these plants are not inherently fraudulent.