Pausinystalia johimbe Seeds | Yohimbe

Yohimbe (Pausinystalia johimbe) with a tall straight trunk, glossy leaves and clusters of small pale flowers — Yohimbe (*Pausinystalia johimbe*): Rubiaceae, the West African forest tree whose bark yields yohimbine, a prescription drug and a serious poison.

LATIN NAME: Pausinystalia johimbe

COMMON NAME: Yohimbe

Plant Profile

Yohimbe is a tall forest tree of the Rubiaceae, ten to thirty metres in maturity, with a straight, cylindrical bole, a buttressed base and a crown of large, glossy, elliptic leaves held in opposite pairs. The bark is grey-brown and slightly fissured on the outside and yellowish within, and it is the part of the tree that matters commercially. The flowers are small, pale and borne in dense clusters, and the fruit is a capsule containing winged seed. The tree is native to the lowland and montane forests of western and central Africa, from Nigeria through Cameroon and Equatorial Guinea to Gabon and Congo-Brazzaville, where it grows in the understorey of humid, closed-canopy forest.

The species is dioecious, with male and female flowers on separate trees, which means that only part of a population bears seed and that the sex of a tree cannot be told until it flowers. It is slow-growing and shade-tolerant as a young plant, reaching the canopy only after decades, and it does not regenerate well in logged or fragmented forest. That combination of slow growth, dioecy and a bark trade that kills the tree has made it a species of conservation concern across its range, and wild harvesting is now regulated in several countries.

Science & Biotechnology

The bark contains a group of indole alkaloids, of which yohimbine is the best known, together with its stereoisomer rauwolscine, corynanthine and related compounds. Yohimbine is an alpha-2 adrenergic antagonist, and that action is the basis of its medical use and of its dangers. By blocking presynaptic alpha-2 receptors it increases sympathetic outflow, which raises heart rate and blood pressure, produces anxiety and tremor, and at higher doses can cause arrhythmias and hypertensive crisis. It is a prescription drug in most countries, used in some for erectile dysfunction and in veterinary medicine as a reversal agent, and it is not a safe self-medication.

The pharmacology has been worked over since the late nineteenth century, and the tree’s chemistry is unusually well documented for an African forest species. Work in the 1990s and 2000s examined yohimbine’s effects on fat metabolism, on anxiety and on autonomic function, and produced a series of case reports of adverse reactions to bark products sold as supplements. Several countries have restricted or banned the sale of yohimbine and yohimbe bark, and the European Union and the United States have both issued warnings. Research on the plant itself now focuses on cultivation, on the sustainability of bark harvesting, and on the genetic diversity of wild populations, which is low in some areas because of selective logging.

Uses & Benefits

The only legitimate use is pharmaceutical, and even there the drug is narrow in its indications and requires medical supervision. The raw bark, sold as a herbal aphrodisiac, is a different matter: the dose of yohimbine in a spoon of bark is unknown, the alkaloid content varies widely, and the margin between a therapeutic and a dangerous dose is small. The plant should not be used at home for any purpose, and it should not be combined with antidepressants, blood pressure medication or stimulants. Anyone who has taken it and experiences palpitations, agitation or chest pain should seek medical help.

In its native range the tree is also used in traditional medicine, particularly in Cameroon and Gabon, where the bark is taken for fatigue and as a sexual tonic, and the wood is used for construction and fuel. Neither use is a reason to grow the tree in a garden, and it is not ornamental in any conventional sense. It is grown in a few botanical collections and research plantations, mainly for study and for the development of sustainable bark production, and it requires a humid tropical climate and deep forest soil to succeed.

Growing from Seed

The seed is small, short-lived and difficult. Sow it fresh on the surface of a loose, humus-rich mix, cover lightly, and keep it at twenty-five to thirty degrees with high humidity and shade. Germination is slow and erratic, often taking two to three months, and the seedlings are delicate for their first year. Sterile technique matters, since damping off is common in the warm, humid conditions the seed requires.

Grow the seedlings on in deep pots of forest soil, in heavy shade, with constant humidity. The tree needs a frost-free tropical climate, deep, well-drained acid soil and shelter from wind, and it will not tolerate drought or exposure. In cultivation it is slow, and it should not be planted out until it is at least a metre tall. Given the legal restrictions on the species in many countries and the conservation status of wild populations, anyone intending to grow it should check the rules that apply where they live before ordering seed.

Our Take

A tree of genuine pharmacological importance and genuine danger, and not a garden plant. Its value now is in conservation and in cultivated pharmaceutical supply, not in the herb shelf.

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