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2 peer-reviewed studies
What the evidence says
Comfrey doesn't have enough studies with structured effect-size data yet to pool a verdict. Browse the studies below for individual findings.
Most evidence is from medium-quality studies published 2000–2020.
Based on 2 studies
Confidence
Very low confidenceBy outcome
Newest study from 2020
In plain English: Their safety has been questioned due to the presence of unsaturated pyrrolizidine alkaloids (PAs).
Avila C et al. · Fitoterapia (2020)
In plain English: Only recently was the use of comfrey leaves recognized as a substantial health hazard with hepatic toxicity in humans and carcinogenic potential.
Stickel F et al. · Public Health Nutr (2000)