This is poisoning from eating shellfish which have eaten a poisonous dinoflagellate (a single-celled algae found mainly in the ocean).

Poisonous Ingredient 

  • A neurotoxin (affects the nervous system) found in the dinoflagellate.

Where Found 

  • mussels  
  • clams  
  • oysters  
  • scallops

From June through October, shellfish are more likely to eat poisonous dinoflagellate.

Note: This list may not be all inclusive.


  • body as a whole       o numbness or tingling around the mouth, lips, tongue, and face       o muscle weakness       o paralysis of the legs and/or arms       o lightheadedness       o headache  
  • respiratory       o stop breathing  
  • gastrointestinal       o nausea       o Vomiting       o abdominal cramps       o diarrhea

Home Treatment 
Shellfish poisoning may be a medical emergency. With sudden or significant symptoms, the person should be taken immediately to an emergency medical facility. You may need to call the local emergency number (such as 911). Otherwise, call Poison Control for appropriate treatment information.

Before Calling Emergency 
Determine the following information:

  • the patient’s age, weight, and condition  
  • the name of the product (ingredients and strengths if known)  
  • the time it was swallowed  
  • the amount swallowed

Poison Control, or a local emergency number 

If the situation is not clear, they will instruct you if it is necessary to take the patient to the hospital.

Bring the contaminated shellfish with you to the emergency room if so instructed.

What to expect at the emergency room 
Some or all of the following procedures may be performed:

  • Use gastric lavage.  
  • Give a cathartic (a bowel evacuator).  
  • Activated charcoal.  
  • Open and maintain an airway if needed.  
  • Treat the symptoms.

Expectations (prognosis) 
Survival past 12 hours usually indicates recovery is likely.
Only a small percentage of people actually die from eating contaminated shellfish.

Johns Hopkins patient information

Last revised: December 6, 2012
by Dave R. Roger, M.D.

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All ArmMed Media material is provided for information only and is neither advice nor a substitute for proper medical care. Consult a qualified healthcare professional who understands your particular history for individual concerns.