Yohimbe

Yohimbe belongs to Rubiaceae, the coffee family, and its naming history explains why searchers meet three versions of its name. Karl Schumann described the tree in 1901, in a Berlin botanical garden bulletin, as Corynanthe johimbe, spelling the epithet with a German j; the International Plant Names Index (IPNI) records that publication. World Flora Online notes a replacement reference specimen (a neotype) collected at Bipinde in southern Cameroon in 1904. The botanist Pierre later concluded that the fruit did not match other Corynanthe species, and in 1906 Beille published the new combination Pausinystalia johimbe, credited to Pierre; IPNI notes that it was first printed as “yohimba.” Pausinystalia became the standard name in pharmacy texts, PROTA, and much of the medical literature. The spelling Pausinystalia yohimbe, used by NCCIH, the European Food Safety Authority (EFSA), and EU law, refers to the same tree with a variant spelling, and EFSA also lists Corynanthe yohimbe among its synonyms. World Flora Online, drawing on data from Kew’s World Checklist, now treats Corynanthe johimbe as the accepted name and Pausinystalia johimbe as a synonym, which is why both names appear on supplement labels and in plant databases.

PROTA describes an evergreen, medium-sized tree up to 30 m tall, occasionally 35 m, with a straight, unbuttressed trunk that rarely exceeds 50–60 cm across and is grooved at the base. The outer bark is grey to reddish brown, split by long furrows and short cross-cracks, and peels off easily; the fibrous inner bark is pinkish and turns reddish brown when exposed to air. The 1918 Dispensatory of the United States compared the fissured bark to old specimens of cinchona. The branches grow in whorls, and the leaves are usually arranged in whorls of three, only rarely in opposite pairs. The leaves are large, obovate or oblanceolate, from about 11 to 47 cm long, with 10 to 20 pairs of side veins and often wavy edges. Fragrant small flowers are borne in branched clusters at the shoot tips; the corolla is usually white or yellowish, sometimes red or purple, and each of its lobes ends in a thread-like appendage 8–20 mm long. The fruit is a small, flattened capsule about 1–1.6 cm long holding many winged seeds, which are dispersed by wind. In PROTA’s account the tree flowers from about August to February.

Yohimbe grows in evergreen lowland forest, both primary and regrowing, and World Flora Online’s Flore d’Afrique Centrale entry gives an elevation range of up to about 800 m. It is a light-demanding species: seedlings survive poorly under a closed canopy, growth is fast in the open, and cut stumps resprout well. Its conservation status is debated. The Flore d’Afrique Centrale entry considers it probably of least concern, known from more than 30 localities including national parks in Gabon and the Republic of the Congo, and often favored by forest clearing. PROTA, however, reports that 1990s inventories in Cameroon and Equatorial Guinea found on average only 4 trees per hectare over 10 cm in diameter, and that demand for the bark has led to over-exploitation. Most traded bark comes from Cameroon, which exported an average of 286 tonnes a year in 1985–1991 and 715 tonnes in the 1997–1998 season. Trees are cut at about 10 cm in trunk diameter and usually felled to strip the bark, which PROTA calls unsustainable; stripping panels from standing trees would let the bark regrow in about two years, though harvesters say stem borers often kill wounded trees anyway.

The medicinal part is the bark of the trunk and branches. PROTA reports up to 6% total alkaloids in the bark, of which yohimbine makes up 10–15%, along with relatives such as corynanthine, alloyohimbine, and ajmalicine; alkaloid levels are highest in the trunk and root bark, lower in branches, very low in leaves, and highest in the rainy season. EFSA’s 2013 review put the yohimbine content of bark at usually around 10 mg per gram, while noting that published figures vary widely with the age of the tree, the height at which bark is taken, and the analytical method. Yohimbine (C21H26N2O3) is not unique to this tree: it is identical to quebrachine, isolated in 1880 from the bark of the South American white quebracho tree. Substitution is a long-standing problem. PROTA warns that yohimbe bark is often adulterated with bark of other Pausinystalia and Corynanthe species with less yohimbine, and suspects that much of Cameroon’s exported bark is really Pausinystalia macroceras. True yohimbe has larger leaves on shorter stalks and bark that is intensely bitter and easy to peel, while P. macroceras bark is less bitter and hard to peel.

Long before it reached a laboratory, yohimbe bark was part of everyday life in the forests of Cameroon and its neighbors. A 1999 history in Germany’s Pharmazeutische Zeitung records local names such as njumbehoa, yumbehoa, and yohimbehe, and early reports that the bark was boiled into a strengthening drink and used by Bantu-speaking peoples as a stimulant and aphrodisiac at wedding celebrations. PROTA lists a wider range of uses: in Gabon small pieces are chewed to stay awake, with larger amounts used as an aphrodisiac; elsewhere the bark has been taken as a local anesthetic, a hallucinogen, for angina, constipation, and intestinal worms, by athletes, and to clear singers’ voices, while in the Republic of the Congo a decoction is drunk for pelvic pain and in Gabon the bark serves as a fish poison. The tree had practical uses too, with young stems used as building poles and inner bark made into straps for hunting baskets. PROTA records the Portuguese name pau de Cabinda and the French name démarreur, meaning “starter.” None of these traditional uses has been tested in modern trials.

European interest began in the German colonial period. Cameroon became a German protectorate in 1884, and according to the Pharmazeutische Zeitung history, the trader Ludwig Scholz, an agent of the Hamburg firm Woermann, probably sent the bark around 1895 to the Chemische Fabrik Güstrow in northern Germany. The firm passed it to the Pharmacological Institute of the University of Berlin, where the chemist Leopold Spiegel isolated the active alkaloid and named it yohimbine after the local names for the tree, publishing his results in 1896. Spiegel asked the botanist Karl Schumann to identify the source; Schumann first placed it in the dogbane family before settling on the coffee family and the name Corynanthe johimbe. Animal experiments published in 1898 produced erections in dogs, but larger doses caused violent convulsions. In 1900 the physician E. Mendel reported treating 40 patients since 1898, with clear benefit in some but no detectable effect in half of those he could follow up. The Güstrow company began selling Yohimbin Spiegel in 1900, and veterinarians soon adopted it for breeding animals.

For much of the twentieth century yohimbine was a mainstream drug. The 1918 Dispensatory of the United States described the hydrochloride salt, given at 5 mg three or four times a day, as widely used by clinicians for impotence of nervous origin, with generally favorable reports, while noting that it was said to be useless when impotence came from organic nerve damage and harmful with chronic inflammation of the sexual organs or prostate. Not everyone was convinced: the same text recorded an experimenter who found no aphrodisiac effect at all, only nausea, salivation, and irritability. Doctors at the time also debated how much of yohimbine’s effect was suggestion. MSKCC notes that yohimbine was widely prescribed for erectile dysfunction until newer drugs, the PDE5 inhibitors, were approved, and the FDA describes it as once used in a prescription erectile dysfunction medication that has since been largely replaced by safer, more effective treatments. In Europe, EFSA found in 2013 that a few countries still had yohimbine tablets authorized for erectile dysfunction, while Germany’s Commission E had issued a negative monograph on the bark itself because of unproven benefit and unpredictable risk.

The supplement era brought a new set of problems. In 1995 Betz and colleagues described yohimbe bark being promoted in the United States as a dietary supplement alternative to anabolic steroids, and found that commercial products contained from less than 0.1 to 489 parts per million of yohimbine, compared with 7,089 in authentic bark, and lacked the bark’s other alkaloids. In California, Kearney and colleagues found that poison center reports of yohimbine-related harm rose from 1.8 to 8.0 per 10,000 adult exposures between 2000 and 2006. Regulators responded at different speeds. A 1989 FDA rule declared that no over-the-counter aphrodisiac ingredient, yohimbine included, was recognized as safe and effective, and from 1990 such products needed drug approval. EFSA concluded in 2013 that it could not identify a safe intake of yohimbe bark in food. The European Commission put yohimbe under scrutiny in 2015 and, after no one submitted safety data, prohibited it in food in 2019. Health Canada treats yohimbine as a prescription drug and has seized unauthorized products labeled to contain it, and Australia classes it as prescription-only.

Yohimbine’s main action is to block alpha-2 adrenergic receptors. Many of these sit on nerve endings and work as a thermostat: when norepinephrine builds up, they switch further release off. Blocking them takes the brake off the sympathetic nervous system, the fight-or-flight system. Shibao and colleagues (Hypertension 2010) describe yohimbine as activating sympathetic outflow from the brain and unrestraining norepinephrine release from nerve endings. Measured in people, the result is a rise in blood pressure; in a study of 172 people given intravenous yohimbine, Le Corre and colleagues (Clinical Pharmacology and Therapeutics 2004) found the rise came mainly from the heart pumping more blood. MSKCC summarizes the proposed sexual effects as increased blood flow into erectile tissue, plus effects on nitric oxide signaling and on spinal reflexes, while PROTA adds dilation of blood vessels in the genital area and easier ejaculation. The same pathway explains the side effects. MSKCC notes that yohimbine provokes anxiety by activating the brain’s noradrenergic stress system. Alpha-2 receptors on fat cells also restrain fat breakdown, which is the basis of the fat-loss claim.

How much yohimbine reaches the blood is unusually unpredictable. Le Corre and colleagues (European Journal of Pharmaceutical Sciences 1999) found that oral yohimbine had an average bioavailability of about 22%, but with a standard deviation almost as large, and EFSA cites reported values from 7% to 87%. After an intravenous dose, yohimbine itself had a half-life of about 1.5 hours, while its active metabolite, 11-hydroxy-yohimbine, lasted almost four times longer; very little leaves unchanged in urine, so the liver does most of the work. In the larger 2004 study, the conversion of yohimbine to 11-hydroxy-yohimbine varied more than 1,000-fold between people, and 17 of 172 showed no conversion at all. The main route appeared to be the liver enzyme CYP2D6, with variants of both CYP2D6 and CYP3A4 needed to predict who metabolized it, and people who did not metabolize yohimbine had greater activation of their sympathetic nervous system. EFSA notes that these differences in liver metabolism may explain why the same dose affects people so differently.

Bark is not a measured dose of yohimbine. Authorized yohimbine hydrochloride tablets in Europe, summarized by EFSA, were taken at 5–10 mg per dose and 10–30 mg a day, and Anderson and colleagues (Journal of Analytical Toxicology 2013) note that typical oral doses of 5–15 mg give blood levels of about 40–400 ng/mL. Bark contains yohimbine alongside related alkaloids such as corynanthine and ajmalicine, which have effects of their own on blood vessels according to PROTA, and the mixture varies from tree to tree. Yohimbine dissolves readily in alcohol but only sparingly in water, according to EFSA, so a homemade tea or decoction extracts an unknown fraction. Yohimbine also works differently from the PDE5 inhibitors, such as sildenafil, that replaced it. Tam and colleagues (Pharmacology and Therapeutics 2001) suggested that yohimbine’s effect might be strengthened by drugs that boost nitric oxide, but that idea was about supervised combination therapy, not about mixing supplements with prescription drugs at home.

Erectile dysfunction is the use with the most research, nearly all of it on the prescription salt rather than the bark. Ernst and Pittler (Journal of Urology 1998) found seven randomized, placebo-controlled trials of yohimbine on its own, of satisfactory overall quality. Men taking yohimbine were more likely to improve than those on placebo, with an odds ratio of 3.85, and serious adverse reactions were infrequent and reversible; the authors concluded that yohimbine was a reasonable first drug to try. Not every trial agreed. Kunelius and colleagues (Urology 1997) gave 29 men with impotence of mixed physical and psychological causes 36 mg of yohimbine hydrochloride a day or placebo for 25 days each in a crossover design: 44% responded on yohimbine and 48% on placebo, and the authors concluded it was no better than placebo. Tam and colleagues (Pharmacology and Therapeutics 2001) reviewed the field and concluded that yohimbine alone has only modest efficacy, while noting that relatively few well-designed studies existed and that it had not been studied in women’s sexual problems.

Where that leaves yohimbe today is clearer than the old trials. MSKCC states that several research bodies judged the evidence for yohimbine weak and that current guidelines do not recommend it for erectile dysfunction. The FDA describes yohimbine as largely replaced by safer, more effective treatments. For supplements, NCCIH says there is not enough research to show they help erectile dysfunction, and that a supplement may not work like the prescription medicine. That caution is supported by what the products contain: if a capsule holds no yohimbine, or several times the amount of a prescription dose, the old trial results do not apply to it. Erectile problems can have physical and psychological causes, and both deserve a proper assessment. For people interested in plants, the site’s guide to herbs for libido compares the evidence for other herbs such as ginseng and maca, none of which is a substitute for a medical assessment.

Fat loss and sports performance are the other big markets. The idea is that blocking alpha-2 receptors on fat cells releases the brake on fat breakdown, and PROTA notes that this effect is real in the laboratory, but that double-blind trials of weight loss have given conflicting results. The most cited human study is small. Ostojic (Research in Sports Medicine 2006) gave 20 professional soccer players 20 mg of yohimbine a day or placebo for 21 days: body fat fell from 9.3% to 7.1% in the yohimbine group, but body weight, muscle mass, and performance did not change. Larger reviews are unenthusiastic. Pittler and Ernst (American Journal of Clinical Nutrition 2004), reviewing weight-loss supplements including yohimbe, found no convincing evidence for any of them and recommended none for over-the-counter use, and Cimolai and Cimolai (Journal of Dietary Supplements 2011) found no conclusive evidence that yohimbine helps bodybuilding, exercise tolerance, physical performance, or body composition. MSKCC finds no data supporting yohimbe for weight loss or athletic performance, and NCCIH lists obesity and athletic performance among the uses without enough evidence.

Yohimbine has some genuine research uses, all under medical supervision with measured doses. In orthostatic hypotension, a disabling drop in blood pressure on standing seen in some nervous system disorders, Shibao and colleagues (Hypertension 2010) studied 31 people with severe autonomic failure: a single 5.4 mg dose raised standing diastolic blood pressure by about 11 mmHg compared with placebo and improved symptoms of near-fainting, whereas the comparison drug, pyridostigmine, did not. In a pilot trial in 26 men with combat-related post-traumatic stress disorder, Tuerk and colleagues (Cognitive Behaviour Therapy 2018) gave one dose of yohimbine or placebo before the first session of exposure therapy; the yohimbine group showed lower heart-rate reactivity to trauma cues a week later and faster improvement in depression, though not in PTSD symptoms. MSKCC lists these and dry mouth as areas where data are limited. These studies used the pure drug in carefully selected patients and do not support self-treatment with supplements.

The many traditional uses recorded by PROTA and EFSA, as a tonic, stimulant, local anesthetic, hallucinogen, and treatment for angina and intestinal worms, have not been tested in modern trials, and some are actively unwise; using a drug that raises heart rate and blood pressure for chest pain is a clear example. Yohimbe is also promoted as a mood booster and general energy supplement, and NCCIH finds no evidence to support those uses either. MSKCC notes that although yohimbine stimulates the nervous system, clinical data do not support its use as a stimulant. In short, there is no condition for which a yohimbe supplement has been shown to work, and the one condition where the purified drug was tested, erectile dysfunction, now has better treatments. Anyone considering yohimbe for sexual problems, weight, energy, or mood should first talk to a clinician, who can look for treatable causes and offer options with known doses and safety records.

Yohimbe is sold as dried bark, either as flat or curved strips up to about 1 m long or ground into powder (PROTA), and as capsules, tablets, and liquid extracts labeled as yohimbe bark, yohimbe extract, or yohimbine hydrochloride. MSKCC lists older chemical names for yohimbine, including aphrodine, corynine, and quebrachine. Many products are blends. Betz and colleagues could not identify bark microscopically in many of the products they tested because they were mixtures of botanicals or extracts with little plant material, and the FDA warns that products sold for sexual enhancement, weight loss, and bodybuilding may contain hidden drugs, including yohimbine, that are not listed on the label. Label accuracy is poor. In the Cohen study, only 11 of 49 brands stated an amount of yohimbine, and in those the actual content ranged from 23% to 147% of the label. EFSA cites another analysis in which most products held 6–50% of the claimed amount, two held 140% and 180%, and liquid products held only 3% and 17%.

There is no established safe dose of yohimbe bark or supplements. EFSA concluded in 2013 that it could not advise on any daily intake of yohimbe bark that would not raise health concerns. For comparison, the prescription yohimbine hydrochloride products EFSA reviewed were dosed at 5–10 mg at a time and 10–30 mg a day for at least eight weeks, much like the 5 mg three or four times a day in the 1918 Dispensatory. Supplements can exceed that. EFSA calculated that taking four tablets a day of the strongest product reported, at 18.8 mg each, would supply about 75 mg of yohimbine, well above the highest medicinal dose. The European medicine labels EFSA summarized also warned that 200 mg of yohimbine hydrochloride had caused poisoning, with seizures, chest pain, and palpitations. Bark preparations are even less predictable. Yohimbine content in bark varies widely, it dissolves poorly in water, and PROTA notes that because alkaloid content varies so much, crude products are even more dangerous than products with a known amount of yohimbine.

Practical points: the safest choice for most people is not to use yohimbe at all. If a clinician recommends yohimbine for a specific condition, it should be a pharmaceutical product with a stated dose, not a bark supplement. Read the full ingredient list of any sexual enhancement, energy, pre-workout, or fat-burning product, since yohimbe or yohimbine is often one ingredient among several stimulants, and avoid products that do not state how much yohimbine they contain. Be wary of products sold online with dramatic claims; the FDA notes that it cannot test every product marketed as a supplement for hidden ingredients. Do not make tea from bark bought online, which may be a different species altogether. Competitive athletes should know that the European prescribing information summarized by EFSA warned that yohimbine use may lead to positive doping tests. Stop at once and seek urgent care for chest pain, a pounding or irregular heartbeat, severe headache, confusion, seizures, or an erection lasting several hours.