Bu Gu Zhi (补骨脂) — Psoralea Fruit TCM Herb | Kidney Yang, Dawn Diarrhea & Vitiligo

At a Glance

Herb: Bu Gu Zhi
Chinese name: 补骨脂 (Bǔ Gǔ Zhī)
Latin name: Fructus Psoraleae
Nature: Very Warm
Taste: Acrid / Bitter
Meridian: Kidney / Spleen
Category: Herbs that Tonify Yang
Introduction: Bu Gu Zhi (补骨脂, Fructus Psoraleae) is the dried ripe fruit of Psoralea corylifolia L. (also known as Babchi or Bakuchiol plant), an annual herb native to India and southern China. The name 补骨脂 — ‘supplement bone fat/marrow’ — points directly to its primary function of tonifying Kidney yang to nourish bone marrow. First recorded in the Tang dynasty (Kaibao Bencao, 10th century), Bu Gu Zhi is one of the warmest and most potent Kidney yang tonics in the materia medica. It excels in three clinical areas: warming Kidney yang for impotence and cold lumbar pain, warming the Spleen and Kidney for dawn diarrhea (Si Shen Wan), and consolidating essence and stopping enuresis. Its principal active compound psoralen is also used in phototherapy (PUVA) for vitiligo and psoriasis.

Tonifies Kidney yang and consolidates essence: Treats impotence, spermatorrhoea, enuresis, and frequent urination from Kidney yang deficiency. 2. Warms the Spleen and stops diarrhea: Combined with Rou Dou Kou, Wu Wei Zi, and Wu Zhu Yu in Si Shen Wan — the classical formula for fifth-watch (dawn) diarrhea from Spleen-Kidney yang deficiency. 3. Strengthens sinews and bones: Supplements the bone marrow (jing) to treat lumbar pain and weakness. 4. Promotes Qi transformation and astringes urine: Reduces urinary frequency and enuresis. 5. Topical applications: Psoralen content promotes melanin synthesis — used topically for vitiligo.

Bu Gu Zhi is one of the most warming kidney tonics — its very warm nature makes it particularly suited for deep Kidney yang deficiency with cold signs: impotence, infertility from cold uterus, persistent dawn diarrhea, and weak cold lumbar spine. In Si Shen Wan (四神丸), it is the lead herb for Spleen-Kidney yang deficiency diarrhea — specifically the fifth-watch (approximately 5 am) diarrhea caused by yang insufficiency unable to warm the Spleen before dawn. Salt-processing (Yan Bu Gu Zhi) is standard — salt directs to the Kidney and moderates the drying heat. Topical Bu Gu Zhi tincture is used in dermatology for vitiligo (leukoderma) — psoralen sensitises melanocytes to UV light, restoring pigmentation.

Contraindicated in yin deficiency fire, excess heat, and constipation from heat or dryness. Avoid in pregnancy — historically used to induce abortion at high doses. Psoralen content causes photosensitivity — caution with sunlight exposure after large oral doses. Do not apply topical psoralen preparations to face without UV protection. Hepatotoxicity reported with very high doses or prolonged use — stay within standard dosage (6–10 g). Salt-processing (Yan Bu Gu Zhi) is standard and reduces heat intensity.

Si Shen Wan (四神丸): Bu Gu Zhi, Rou Dou Kou, Wu Wei Zi, Wu Zhu Yu, Sheng Jiang, Da Zao.
Qing E Wan (青蛾丸): Bu Gu Zhi, Du Zhong, Hu Tao Ren — Kidney yang lumbar pain.
Er Shen Wan (二神丸): Bu Gu Zhi, Rou Dou Kou — simple Spleen-Kidney diarrhea formula.

Bu Gu Zhi + Rou Dou Kou + Wu Wei Zi + Wu Zhu Yu (Si Shen Wan): Spleen-Kidney yang deficiency with dawn diarrhea. Source: Restoration of Health from Myriad Diseases (万病回春).
Bu Gu Zhi + Du Zhong + Hu Tao Ren (Qing E Wan): Kidney yang deficiency with lumbar pain, weakness, and cold. Source: Beneficial Formulas from the Taiping Imperial Pharmacy (太平惠民和剂局方).
Bu Gu Zhi + Yin Yang Huo + Tu Si Zi + Shu Di Huang: Kidney yang and essence deficiency — impotence and cold infertility. Source: Classical tonic formula tradition.
Bu Gu Zhi + Tu Si Zi + Wu Wei Zi: Spermatorrhoea and enuresis from Kidney qi failing to consolidate. Source: Jin Suo Gu Jing Wan family.
Bu Gu Zhi (topical tincture): Applied directly to vitiligo patches — promotes melanin synthesis. Modern dermatological application.

Multiple studies confirm Bu Gu Zhi extracts
- Bone-protective: increase bone mineral density, promote osteoblast differentiation, and inhibit osteoclastogenesis in osteoporosis models
Dermatological
- Psoralen sensitises melanocytes to UV light (PUVA therapy) — widely used clinically for vitiligo and psoriasis
Strong antioxidant
- Bakuchiol: promotes collagen synthesis — anti-ageing cosmetic applications
Isoflavone fractions
- Oestrogen-like activity: bind oestrogen receptors — may explain beneficial effects in menopausal bone loss
Extracts
- Antidepressant: demonstrate antidepressant-like effects in rodent models via monoamine pathways

《开宝本草》(Kaibao Bencao, 974 CE): ‘补骨脂，主五劳七伤，风虚冷，骨髓伤败，肾冷精流，及妇人血气堕胎。’ (Bu Gu Zhi governs the five taxations and seven damages, wind-vacuity cold, bone marrow damage and deterioration, Kidney cold with seminal leakage, and in women blood-qi miscarriage.)
《本草纲目》(Bencao Gangmu, 1596): ‘补骨脂，能暖水脏，阴中生阳，壮火益土之要药也。’ (Bu Gu Zhi can warm the water organ (Kidney); it generates yang within yin — the essential herb for strengthening fire and benefiting earth.)
《本草经疏》(Bencao Jingshu, 1625): ‘补骨脂，气大温，味辛苦，无毒，能暖肾脏，壮元阳，治命门火衰之证，为温补命门之要品。’ (Bu Gu Zhi: greatly warm qi, acrid-bitter flavour, non-toxic. Can warm the Kidney organ, fortify original yang, and treat patterns of declining Gate of Life fire — the essential item for warming and supplementing the Gate of Life.)