Pet Safety / Compounds / Microcystin-LR

Is Microcystin-LR safe for dogs and cats?

Extreme risk for pets

Microcystin-LR (MC-LR) is a cyclic heptapeptide hepatotoxin produced by cyanobacteria (blue-green algae), predominantly Microcystis aeruginosa, during harmful algal blooms (HABs) in freshwater lakes, ponds, and reservoirs. Dogs are the most commonly and severely affected companion animals from HAB exposure, primarily because dogs swim in and drink bloom-affected water during outdoor activities. Mechanism: microcystin inhibits protein phosphatases PP1 and PP2A → uncontrolled phosphorylation of cytoskeletal and regulatory proteins → acute hepatocellular necrosis. Onset: clinical signs appear within 30 minutes to hours of significant exposure. Signs: profuse vomiting, bloody diarrhea, weakness, jaundice, seizures, coma, and rapid death in severe cases. Dozens to hundreds of dog deaths are reported annually across the US, with notable cluster events (North Carolina, Kansas, Georgia, Texas) in hot, dry summers when algal blooms intensify. Death can occur within hours of exposure. There is no specific antidote. Treatment: aggressive supportive care, liver protectants (SAMe, silymarin), vitamin E antioxidant therapy, fluid resuscitation. HAB-affected water is visually distinctive (green/blue-green scum, paint-like surface) but dogs do not discriminate and owners may not recognize the hazard. Health departments in 41 US states now issue HAB advisory alerts. Dogs should be immediately washed if they contact suspected bloom-affected water, and any clinical signs warrant emergency veterinary care.

What is microcystin-lr?

The IUPAC name is (5R,8S,11R,12S,15S,18S,19S,22R)-15-[3-(diaminomethylideneamino)propyl]-18-[(1E,3E,5S,6S)-6-methoxy-3,5-dimethyl-7-phenylhepta-1,3-dienyl]-1,5,12,19-tetramethyl-2-methylidene-8-(2-methylpropyl)-3,6,9,13,16,20,25-heptaoxo-1,4,7,10,14,17,21-heptazacyclopentacosane-11,22-dicarboxylic acid.

Also known as: (5R,8S,11R,12S,15S,18S,19S,22R)-15-[3-(diaminomethylideneamino)propyl]-18-[(1E,3E,5S,6S)-6-methoxy-3,5-dimethyl-7-phenylhepta-1,3-dienyl]-1,5,12,19-tetramethyl-2-methylidene-8-(2-methylpropyl)-3,6,9,13,16,20,25-heptaoxo-1,4,7,10,14,17,21-heptazacyclopentacosane-11,22-dicarboxylic acid, Microcystin LR, Cyanoginosin LR, Cyanoginosin-LR.

IUPAC name
(5R,8S,11R,12S,15S,18S,19S,22R)-15-[3-(diaminomethylideneamino)propyl]-18-[(1E,3E,5S,6S)-6-methoxy-3,5-dimethyl-7-phenylhepta-1,3-dienyl]-1,5,12,19-tetramethyl-2-methylidene-8-(2-methylpropyl)-3,6,9,13,16,20,25-heptaoxo-1,4,7,10,14,17,21-heptazacyclopentacosane-11,22-dicarboxylic acid
CAS number
101043-37-2
Molecular formula
C49H74N10O12
Molecular weight
995.2 g/mol
SMILES
CC1C(NC(=O)C(NC(=O)C(C(NC(=O)C(NC(=O)C(NC(=O)C(=C)N(C(=O)CCC(NC1=O)C(=O)O)C)C)CC(C)C)C(=O)O)C)CCCN=C(N)N)C=CC(=CC(C)C(CC2=CC=CC=C2)OC)C
PubChem CID
445434

Risk for dogs

Extreme risk

Microcystin-LR (MC-LR) is a cyclic heptapeptide hepatotoxin produced by cyanobacteria (blue-green algae), predominantly Microcystis aeruginosa, during harmful algal blooms (HABs) in freshwater lakes, ponds, and reservoirs. Dogs are the most commonly and severely affected companion animals from HAB exposure, primarily because dogs swim in and drink bloom-affected water during outdoor activities. Mechanism: microcystin inhibits protein phosphatases PP1 and PP2A → uncontrolled phosphorylation of cytoskeletal and regulatory proteins → acute hepatocellular necrosis. Onset: clinical signs appear within 30 minutes to hours of significant exposure. Signs: profuse vomiting, bloody diarrhea, weakness, jaundice, seizures, coma, and rapid death in severe cases. Dozens to hundreds of dog deaths are reported annually across the US, with notable cluster events (North Carolina, Kansas, Georgia, Texas) in hot, dry summers when algal blooms intensify. Death can occur within hours of exposure. There is no specific antidote. Treatment: aggressive supportive care, liver protectants (SAMe, silymarin), vitamin E antioxidant therapy, fluid resuscitation. HAB-affected water is visually distinctive (green/blue-green scum, paint-like surface) but dogs do not discriminate and owners may not recognize the hazard. Health departments in 41 US states now issue HAB advisory alerts. Dogs should be immediately washed if they contact suspected bloom-affected water, and any clinical signs warrant emergency veterinary care.

Regulatory consensus

1 regulatory bodyhas classified Microcystin-LR.

AgencyYearClassificationNotes
EPA CTX / IARC—Group 2B - Possibly carcinogenic to humans

Regulators apply different standards of evidence — animal-data weighting, exposure-pattern assumptions, epidemiological power thresholds — which is why two scientific bodies can review the same data and reach different conclusions. The disagreement is the data.

Where pets encounter microcystin-lr

  • Industrial Facilities — Manufacturing plants, Chemical storage areas, Waste treatment sites
  • Occupational Environments — Factories, Warehouses, Transportation vehicles

Safer alternatives

Lower-risk approaches that achieve a similar outcome to Microcystin-LR:

  • Avoidance (no chemical substitute)
    Trade-offs: Direct chemical substitution requires verification that the replacement does not introduce new hazards (regrettable substitution). Conduct full hazard assessment of proposed alternative before adoption.
    Relative cost: 1.2-2×

Frequently asked questions

Is microcystin-lr safe for pets?

Microcystin-LR (MC-LR) is a cyclic heptapeptide hepatotoxin produced by cyanobacteria (blue-green algae), predominantly Microcystis aeruginosa, during harmful algal blooms (HABs) in freshwater lakes, ponds, and reservoirs. Dogs are the most commonly and severely affected companion animals from HAB exposure, primarily because dogs swim in and drink bloom-affected water during outdoor activities. Mechanism: microcystin inhibits protein phosphatases PP1 and PP2A → uncontrolled phosphorylation of cytoskeletal and regulatory proteins → acute hepatocellular necrosis. Onset: clinical signs appear within 30 minutes to hours of significant exposure. Signs: profuse vomiting, bloody diarrhea, weakness, jaundice, seizures, coma, and rapid death in severe cases. Dozens to hundreds of dog deaths are reported annually across the US, with notable cluster events (North Carolina, Kansas, Georgia, Texas) in hot, dry summers when algal blooms intensify. Death can occur within hours of exposure. There is no specific antidote. Treatment: aggressive supportive care, liver protectants (SAMe, silymarin), vitamin E antioxidant therapy, fluid resuscitation. HAB-affected water is visually distinctive (green/blue-green scum, paint-like surface) but dogs do not discriminate and owners may not recognize the hazard. Health departments in 41 US states now issue HAB advisory alerts. Dogs should be immediately washed if they contact suspected bloom-affected water, and any clinical signs warrant emergency veterinary care.

What products contain microcystin-lr?

Microcystin-LR appears in: Manufacturing plants (Industrial facilities); Chemical storage areas (Industrial facilities); Factories (Occupational environments); Warehouses (Occupational environments).

See Microcystin-LR in the pets app

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Sources (4)
  1. ASPCA Animal Poison Control Center: Cyanobacterial (Blue-Green Algae) Toxicosis in Companion Animals — Microcystin Hepatotoxicity (2022) — report
  2. US EPA: Cyanotoxins in Drinking Water — Health Advisories for Microcystins and Cylindrospermopsin (2015) — regulatory
  3. WHO: Cyanobacterial Toxins — Microcystin-LR in Drinking Water: Background Document for Development of WHO Guidelines (2003) — regulatory
  4. IARC Monographs Volume 134: Microcystin-LR — Group 2B Evaluation (Possibly Carcinogenic to Humans) (2018) — regulatory

Reference data, not professional advice. Aggregates publicly available regulatory and scientific data; not a substitute for veterinary, medical, legal, or regulatory advice. Why we built ALETHEIA →