Cooper, M.R., Johnson, A.W. & Dauncey, E.A. 2003. Poisonous plants and fungi: an illustrated guide. London: TSO 2 nd edition.
Although there is very little evidence, it appears that eating Leyland cypress can cause serious poisoning in animals. It has caused serious digestive system disturbances and extreme weakness in horses and cattle........ Veterinary advice may be required.
Cooper, M.R. & Johnson, A.W. 1998. Poisonous plants and fungi in Britain: animal and human poisoning. London: The Stationary Office
Poisonous principles
Little is known about these, but Leyland Cypress is thought to contain terpenes and phenol derivatives present in the parent trees.
Animal poisoning
From the few cases that have been reported, it appears that Leyland cypress can cause serious poisoning. Weakness, depression, trembling and loss of appetitie have been reported in horses, scouring and rectal prolapse in cattle and hypersalivation and death in goats (NPIS, London, personal communication).
Poisonous principles
Various terpenes, pinenes and phenol derivatives are present, as well as some essential oils.
Animal poisoning
Poisoning by Cupressus has been reported mainly in cattle (Long, H.C. 1917 Plants poisonous to livestock.Cambridge University Press, Cambridge; and MacDonald, J.
1956 Macrocarpa poisoning, New Zealand Veterinary Journal 4: 30), in which loss of condition, weakness, staggering gait, and sunken eyes are consistently found. The foliage and woody parts of felled cypress trees ( Cupressus sempervirens ) were responsible for the death of two heifers in Britain (Gould, C.M. 1962 Cypress poisoning, Veterinary Record 74:743), and a cow in Ireland that ate trimmings from a cypress hedge ( Cupressus macrocarpa ) became dull and slightly bloated and was found dead among the felled branches the next day, the animal was eight months pregnant (O’Scanall, T. 1986, Suspected cypress poisoning in a cow, Irish Veterinary

Journal 40:156). A large quantity of foliage was found in the rumen, and there was blood-stained fluid in the abdominal cavity. The other 18 animals grazing in the same field were apparently unaffected, although some were seen eating the cypress trimmings. [This reference also provides further details on induction of abortion in cows and cerebral leukoencephalomalacia in foetuses on post-mortem examination.]
Bruneton, J. 1999, Toxic plants dangerous to humans and animals, Lavoisier, Paris.
Has a little more information on isocupressic acid in Cupressus relating to abortion in cows.

Extract from:
Poisonous Plants and Fungi in Britain and Ireland © Medical Toxicology Unit of Guy's and St Thomas' Hospital NHS Trust and the Royal Botanic Gardens, Kew, 1995-2000
Latin name: CUPRESSOCYPARIS LEYLANDII
Common name: LEYLAND CYPRESS
Family: Cupressaceae
DESCRIPTION
This species is an intergeneric hybrid, first raised in 1888 at Leighton Hall, Welshpool, from seed taken from a tree of Chamaecyparis nootkatensis which had been fertilised by pollen from a tree of
Cupressus macrocarpa growing nearby.
DESCRIPTION: Extremely vigorous, dense, evergreen tree up to c. 35 m high with a columnar to conic or sometimes flame-shaped crown which is tapered towards the top and bent to one side, and often with ascending branches arranged in a compact system; probably the most widely grown shelter-belt tree in Britain.
TRUNK: circumference normally up to c. 1 m (occasionally to 4 m), rarely forked; bark thin to thickish, dark red-brown or brown sometimes tinged green, often smooth at first becoming stringy with shallow, often broad, vertical fissures, sometimes peeling.
BRANCHLETS: flattened or somewhat quadrangular, slightly drooping.
LEAVES: scale-like, 1.5-2 mm long, overlapping, keeled, pointed at the apex, slightly incurved, dark green, blue-green, grey-green or gold-yellow above, yellow-green, blue-green or grey-green below, occasionally variegated with white, faintly aromatic when crushed.
CONES: female cones 1-3 cm across, rounded, green at first ripening to dark shiny brown, maturing in 1-2 years, scales usually 8, with a small, central bump; male cones ovoid, to 3 mm long.
SEEDS: c. 5 on each scale, c. 5 mm wide, warty, with 2 broad even wings.
TOXICITY
Author: Nicola Bates, National Poisons Information Service (London)
Circumstances of exposure: Vigorous, evergreen trees used widely for hedging. Skin contact may occur during pruning or planting and children may accidentally chew or ingest plant material.
Poisonous parts: All parts.
Main toxins: Not known.
Summary: Cupressocyparis leylandii contains allergenic compounds, and skin contact may result in dermatitis. Acute ingestion may result in gastrointestinal symptoms.
Toxicity
The identity of the allergens in Cupressocyparis leylandii is unknown, but most are shared, or crossreact, with colophony (Hindson et al., 1982; Lovell et al., 1985). Colophony or rosin is the residue left

after distilling the volatile oil from various species of Pinus. It has many uses (listed in Lovell, 1993) including adhesive plasters for wound dressing. It is possible that dermatitis from exposure to
Cupressocyparis leylandii occurs in individuals previously sensitised by adhesive plaster (Lovell,
1993). It is not known whether Cupressocyparis leylandii may itself sensitise (Lovell, 1993).
Clinical effects
Ingestion: No specific data, but may cause mild gastrointestinal upset.
Dermal: Contact dermatitis may occur (Hindson et al., 1982; Lovell et al., 1985; Lovell, 1993).
Individuals sensitive to colophony may develop dermatitis following exposure to Cupressocyparis leylandii.
Case reports
A 48-year-old man wearing a short-sleeved shirt pruned a hedge of Cupressocyparis leylandii and within 24 hours developed linear erythematous streaks on the flexor forearms and erythema of the face. He had reacted to sticking plaster in the past and noticed redness and itching of his face on a previous occasion when working near the hedge. Patch tests were positive for colophony, Spanish colophony and Cupressocyparis leylandii (Lovell et al., 1985).
A 40-year-old man known to react to sticking plaster developed acute eczema of his face, hands and arms 2 days after planting about 100 Cupressocyparis leylandii plants. Patch tests were positive for
Spanish colophony, zinc oxide plaster (containing colophony) and Cupressocyparis leylandii
(Hindson et al., 1982).
Treatment
MEDICAL TREATMENT:
Ingestion: Gastric decontamination is not required. Oral fluids may be given as necessary.
Management is symptomatic and supportive.
Dermal: Treatment is symptomatic and supportive.
If serious or unexplained symptoms occur, medical professionals should contact the National Poisons
Information Service.
GENERAL EMERGENCY AID:The following advice is a GENERAL GUIDE to assist the public in the first steps of managing a suspected poisoning. It has not been tailored for this particular plant.
Medical attention should be sought if poisoning is suspected.
If you suspect possible poisoning from EATING a plant:
* DO NOT try to make the person sick;
* a single glass of milk may be helpful, but if the person is unconscious or fitting do not give anything by mouth;
* IMMEDIATELY take the person to a doctor or hospital Accident and Emergency or Casualty
Department;
* note the NAME of the plant if you think you have identified it, and TAKE a good specimen with you, i.e. a large piece of plant including leaves, fruits and flowers if present.
* note TIME of eating and the onset of any symptoms, which may appear some time later.
If a SKIN or EYE reaction to a plant is suspected:
* WASH the affected area with clean water;
* protect skin from sunlight;

* seek MEDICAL attention if symptoms develop;
* note the NAME of the plant if you think you have identified it, and TAKE a good specimen with you, i.e. a large piece of plant including leaves, fruits and flowers if present.
* note TIME of contact and the onset of any symptoms, which may appear some time later.
References
Hindson, C., Lawlor, F. and Downey, A. (1982). Cross sensitivity between zinc oxide plaster and
Cupressus leylandii shrubs. Contact Dermatitis 8: 335.
Lovell, C. R. (1993). Plants and the Skin. Blackwell Scientific Publications: London.
Lovell, C. R., Dannaker, C. J. and White, I. R. (1985). Dermatitis from X Cupressocyparis leylandii and concomitant sensitivity to colophony. Contact Dermatitis 13(5): 344-345.
Poisonous Plants and Fungi in Britain and Ireland © Medical Toxicology Unit of Guy's and St Thomas' Hospital NHS Trust and the Royal Botanic Gardens, Kew, 1995-2000

Extract from:
Dauncey E. (ed) (2000 updated 14 March 2003). Revision of the Horticultural Trades
Association Code of Practice for the labelling of potentially harmful plants. REPORT A, B, C taxa AND D (label not required), and taxa not previously considered. Medical Toxicology Unit,
Guy's & St Thomas' Hospital Trust and Royal Botanic Gardens, Kew. (Toxicity Authors:
Marion Cooper, Tony Johnson and Nicola Bates and other staff of the National Poisons Information
Service (London). Toxicity Editors: Nicola Bates, Nicholas Edwards, Margot Nicholls, Frances
Northall, Hew Prendergast. Consultant Toxicologist: Virginia S. G. Murray. Assistant Editors, Royal
Botanic Gardens, Kew: Jill Turner and Sasha Barrow).
Latin name: X CUPRESSOCYPARIS LEYLANDII (Dallim. and A.B.Jacks.) Dallim .
Common name: LEYLAND CYPRESS
Family: Cupressaceae
Category in HTA Code (1994) and (2000): C, May cause skin allergy
This species is an intergeneric hybrid, first raised in 1888 at Leighton Hall, Welshpool, from seed taken from a tree of Chamaecyparis nootkatensis (D. Don) Sudw. which had been fertilised by pollen from a tree of Cupressus macrocarpa Hartw. growing nearby.
Circumstances of exposure: Vigorous, evergreen trees used widely for hedging. Skin contact may occur during pruning or planting and children may accidentally chew or ingest plant material.
Poisonous parts: All parts.
Main toxins: Not known.
Summary: Cupressocyparis leylandii contains allergenic compounds, and skin contact may result in dermatitis. Acute ingestion may result in gastrointestinal symptoms,
Author: Nicola Bates
Toxicity
The identity of the allergens in Cupressocyparis leylandii is unknown, but most are shared, or crossreact, with colophony (Hindson et al.
, 1982; Lovell et al.
, 1985). Colophony or rosin is the residue left after distilling the volatile oil from various species of Pinus . It has many uses (listed in Lovell, 1993) including adhesive plasters for wound dressing. It is possible that dermatitis from exposure to
Cupressocyparis leylandii occurs in individuals previously sensitised by adhesive plaster (Lovell,
1993). It is not known whether Cupressocyparis leylandii may itself sensitise (Lovell, 1993).
Clinical effects
Ingestion: No specific data, but may cause mild gastrointestinal upset.
Dermal: Contact dermatitis may occur (Hindson et al.
, 1982; Lovell et al.
, 1985; Lovell, 1993).
Individuals sensitive to colophony may develop dermatitis following exposure to Cupressocyparis leylandii .
Case reports
A 48-year-old man wearing a short-sleeved shirt pruned a hedge of Cupressocyparis leylandii and within 24 hours developed linear erythematous streaks on the flexor forearms and erythema of the face. He had reacted to sticking plaster in the past and noticed redness and itching of his face on a

previous occasion when working near the hedge. Patch tests were positive for colophony, Spanish colophony and Cupressocyparis leylandii (Lovell et al.
, 1985).
A 40-year-old man known to react to sticking plaster developed acute eczema of his face, hands and arms 2 days after planting about 100 Cupressocyparis leylandii plants. Patch tests were positive for
Spanish colophony, zinc oxide plaster (containing colophony) and Cupressocyparis leylandii
(Hindson et al.
, 1982).
References
Hindson, C., Lawlor, F. and Downey, A. (1982). Cross sensitivity between zinc oxide plaster and
Cupressus leylandii shrubs. Contact Dermatitis 8: 335.
Lovell, C. R. (1993). Plants and the Skin. Blackwell Scientific Publications: London.
Lovell, C. R., Dannaker, C. J. and White, I. R. (1985). Dermatitis from X Cupressocyparis leylandii and concomitant sensitivity to colophony. Contact Dermatitis 13(5): 344-345.