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Chasteberry for horses with PPID: what the guideline says
How the veterinary guideline assesses chasteberry (monk's pepper) in PPID (Cushing's disease), why pergolide remains the standard treatment, what is known about interactions and what applies in competitive sport.
The short answer
Chasteberry is mainly fed to horses with PPID (Cushing's disease). The British veterinary guideline sees no effect on the hormone ACTH and no benefit as an addition to pergolide; it rates the evidence as low 1. The standard treatment is daily pergolide 2. If you still want to feed chasteberry, agree this with your vet first.
What chasteberry is
Chasteberry (monk's pepper) is the fruit of the chaste tree (Vitex agnus-castus). For humans, the EU medicines agency describes possible dopaminergic and oestrogenic effects 3.
In horses, chasteberry is mainly fed in connection with PPID, an age-related, slowly progressive disease often called Cushing's 2.
How the guideline assesses the studies
The guideline of the British Equine Veterinary Association assessed the existing studies according to a fixed scheme 1.
- The studies are small and have no untreated control group 1.
- Assessment was often done by the owners 1.
- In one study, the condition of 13 of 14 horses treated with chasteberry deteriorated 1.
| Question | Assessment |
|---|---|
| Clinical signs | possible, data contradictory |
| ACTH | no effect |
| Addition to pergolide | no benefit |
| Evidence | low, recommendation weak |
Assessment of chasteberry in PPID in the BEVA guideline 1.
Interactions with medication
For humans, the EU monograph does not rule out interactions with dopamine agonists 3. Pergolide is a dopamine agonist 2. Whether this applies to horses has not been investigated.
If your horse is on pergolide, discuss any additional herbs with your vet first. This also applies to mixes in which chasteberry is only one ingredient.
Chasteberry in competitive sport
The compounds in chasteberry are not named on the 2025 FEI list, but the list also covers substances with a similar effect 4. The FN bans phytotherapeutics in competition in general 5. Check the ADMR database before competitions 6. Pergolide itself is a medicine whose competition rules you should clarify with your vet.
Key takeaways
- The BEVA guideline rates chasteberry in PPID with low evidence and a weak recommendation 1.
- Pergolide is so far the only medication with a proven reduction in ACTH 7.
- According to the Equine Endocrinology Group, there is no proof of efficacy for complementary feeds in PPID 2.
- In humans, interactions with dopamine agonists cannot be ruled out; pergolide is one 32.
Frequently asked questions
Does chasteberry help with Cushing's?
That is not proven. The BEVA guideline finds no effect on ACTH and no benefit in addition to pergolide 1. PPID needs veterinary treatment.
Can I give chasteberry instead of pergolide?
No, not as a replacement. Pergolide is the only medication with a proven reduction in ACTH in PPID 7. Your vet decides on the treatment.
Does chasteberry help with stomach problems?
We have not found any study on this in horses. Stomach problems should be investigated by your vet before you choose a herb.
Sources & studies
The content is based on the references listed below. It does not replace individual veterinary or feeding advice.
Show list of sources (7)
- Menzies-Gow NJ, Banse HE, Duff A, Hart N, Ireland JL, Knowles EJ, McFarlane D, Rendle D (2023): BEVA primary care clinical guidelines: Diagnosis and management of equine pituitary pars intermedia dysfunction. Equine Veterinary Journal, doi:10.1111/evj.14009Veterinary guideline of the British Equine Veterinary Association with GRADE assessment. Section 3.6.6 and Table 10: chasteberry may improve individual clinical signs but has no demonstrated effect on ACTH. No benefit as an addition to pergolide. Evidence “Low”, recommendation “Weak”. The studies are small, without an untreated control group and with owner assessment; in a third study 13 of 14 horses treated with Vitex deteriorated
- Hart K, Bamford N, Bertin FR, Durham A, Frank N, McGowan C, Schott H (Equine Endocrinology Group, 2025): Recommendations for the Diagnosis and Management of Pituitary Pars Intermedia Dysfunction (PPID). Revised October 2025Veterinary expert recommendation, checked on 30 September 2026. Summary: age-related, slowly progressive disease; prevalence 20% in equids over 15 years, 30% in those over 30 years; hypertrichosis as the classic sign; diagnosis via ACTH, to be interpreted according to season; treatment with daily medication plus feeding management and wellness care. Table 1: clinical spectrum (incl. muscle wasting, polyuria/polydipsia, recurrent infections, HAL). Table 4: choice of feed by body condition and insulin status; with normal insulin status (dynamic test) no carbohydrate restriction needed; many PPID horses lean or with muscle wasting – more fat, protein and energy; frequent BCS checks; dental care, hoof care, parasite control; good quality of life, life expectancy not necessarily shortened. Table 5: efficacy of complementary feeds in PPID not scientifically demonstrated. Recommendation for vets, not a guide for owners.
- European Medicines Agency, HMPC (2018): European Union herbal monograph on Vitex agnus-castus L., fructus, Revision 1. EMA/HMPC/606742/2017Human medicinal monograph, adopted on 27 March 2018. Because of possible dopaminergic and oestrogenic effects, interactions with dopamine agonists and dopamine antagonists cannot be ruled out (4.5). With a history of pituitary disease, seek medical advice beforehand (4.4). Not transferable to horses – context for the advice to agree any combination with pergolide (a dopamine agonist) with your vet
- FEI (2024): 2025 Equine Prohibited Substances List. Fédération Équestre Internationale, Lausanne, Stand 25.11.2024Version checked: 2025 (the 2026 version could not be accessed on 18 October 2026). Harpagoside is listed as CONTROLLED (analgesic), valerenic acid as CONTROLLED, capsaicin as BANNED. Silibinin/silymarin, Vitex constituents (agnuside, casticin), nettle, rosehip and ascorbic acid are not listed by name. Catch-all clause: substances with a similar chemical structure or similar biological effect are also prohibited. The list is revised annually; the current version always applies
- Deutsche Reiterliche Vereinigung (FN): Anti-Doping- und Medikamentenkontroll-Regeln für den Pferdesport (ADMR) mit Verbotsliste Anhang I–IIIRulebook with its own FN prohibited list (Art. 4.1). Annex II (prohibited medication, banned in competition) explicitly names “Harpagophytum Procumbens (Teufelskralle)” (devil's claw) under the musculoskeletal system and, under “Darüber hinaus sind verboten” (also prohibited), lists in general terms “Phytotherapeutika, wie z.B. Arnika, Ingwer” (phytotherapeutics such as arnica, ginger). Catch-all clause for substances with a similar structure or effect. Responsible persons are personally liable for everything administered to the horse (Art. 2.1.1), including with contaminated feed supplements (commentary on Art. 10.4). The document bears no date
- FN – Anti-Doping und Medikation (ADMR-Suchmaschine)Official database of the FN (German Equestrian Federation) on substances and withdrawal periods in competitive sport
- Kritchevsky JE (2024): Hypertrichosis Associated with Adenomas of the Pars Intermedia. Merck Veterinary ManualSpecialist overview, full review September 2024, updated May 2025: PPID is controlled with oral pergolide. Pergolide is currently the only drug with a demonstrated reduction of endogenous ACTH in PPID. Does not mention chasteberry