Russian comfrey can be considered as a toxic plant, and some comfrey products have been banned for human consumption in some countries (Stickel et al., 2000). It contains at least eight pyrrolizidine alkaloids which cause acute necrosis of liver and lungs in cattle and horses. Administration of comfrey pyrrolizidine alkaloids to rats resulted in liver damage and death (Culvenor et al., 1980). Cases of horse poisoning from Russian comfrey have been reported (Fuller et al., 1986). However, it should be noted that feeding trials with Russian comfrey do not mention toxicity issues.
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