Celery may increase the risk of bleeding or potentiate the effects of warfarin therapy.

– Am J Health Syst Pharm 2000 Jul 1;57(13):1221-7; quiz 1228-30 —
Potential interactions between alternative therapies and warfarin. — Heck AM, DeWitt BA, Lukes AL. — School of Pharmacy and Pharmacal Sciences, Purdue University, Indianapolis, IN, USA.

Celery root is a frequent cause of food allergy in pollen-sensitized patients. Because of problems in blinding challenges with fresh vegetables and the risk of anaphylactic reactions, no double-blind, placebo-controlled, food challenges (DBPCFCs) with celery have been published so far. The aim of the study was to confirm the clinical relevance of celery as a food allergen by DBPCFCs and to evaluate current diagnostic procedures in patients with true allergy.This study confirms the importance of celery as a food allergen for use in DBPCFCs.
– J Allergy Clin Immunol 2000 Aug;106(2):373-8 — Celery allergy confirmed by double-blind, placebo-controlled food challenge: a clinical study in 32 subjects with a history of adverse reactions to celery root. — Ballmer-Weber BK, Vieths S, Luttkopf D, Heuschmann P, Wuthrich B.

Allergic reactions in children.
– Pediatr Med Chir 1995 Nov-Dec;17(6):525-30 — Diagnosis of food allergy caused by fruit and vegetables in children with atopic dermatitis — Ottolenghi A, De Chiara A, Arrigoni S, Terracciano L, De Amici M.

Celery is known to contain psoralens, a group of substances that cause a toxic dermal reaction on exposure to ultraviolet A rays (UVA).
– Int J Dermatol 1994 Feb;33(2):116-8 — An outbreak of phytophotodermatitis due to celery. — Finkelstein E, Afek U, Gross E, Aharoni N, Rosenberg L, Halevy S.

The specific symptoms induced by eating celery were attacks of urticaria and angio oedema, respiratory complaints, systemic anaphylaxis with vascular collapse.
– Clin Allergy 1985 May;15(3):273-9 — Celery sensitivity: clinical and immunological correlations with pollen allergy. — Pauli G, Bessot JC, Dietemann-Molard A, Braun PA, Thierry R.