Paraquat lung

Paraquat lung is a lung disease caused by the weed killer Paraquat (dipyridylium).

Causes, incidence, and risk factors

Paraquat is a weed killer once promoted by the United States for use in Mexico to destroy marijuana plants. Research found that this herbicide was dangerous both to workers who applied it to the plants and to people who smoked the marijuana harvested from them.

Paraquat is now banned in the United States, although it is still legal for some uses in Mexico. As most marijuana smoked in the U.S. is now domestically grown, the risk of paraquat lung to American marijuana smokers is minimal.

Paraquat may cause lung damage by inhalation, it may cause esophageal erosions or ulcers from ingestion and absorption through the gut, or it can cause skin breakdown through contact with intact skin.

Severe ingestion of Paraquat can rapidly cause death from respiratory failure due to a form of proliferative alveolitis, or inflammation of the air spaces in the lungs. This impairs oxygen transport to the blood and may lead to acute respiratory distress syndrome (ARDS).

Administering oxygen to improve the blood oxygen level may actually increase the damage to the lung in such cases of ARDS. Chronic exposure to Paraquat, may cause pulmonary fibrosis, or a stiffening of the lung tissue.

Paraquat may also damage the kidneys, liver, mouth, and esophagus. Death may occur from perforation of the esophagus, or from acute inflammation of the mediastinum, the area that encases major blood vessels and airways in the middle of the chest.


  • Shortness of breath  
  • difficulty breathing  
  • breathing requires increasing effort  
  • sore throat  
  • Vomiting or GI distress

Signs and tests

  • history of exposure to Paraquat  
  • history of marijuana Smoking in the 1970’s


  • arterial blood gasses (abnormal results)  
  • X-ray of the chest  
  • electrolytes (see Chem-20)  
  • urinalysis  
  • BUN  
  • creatinine  
  • pulmonary function tests  
  • urine toxicology screen

There is no specific treatment for Paraquat poisoning. The goal is to relieve symptoms and address any complications that arise.

Expectations (prognosis)
The outcome depends on the severity of exposure. The affected person may develop mild breathing-related symptoms with full recovery, or they may have permanent changes in the lungs, or if the person received a large dose at once (as with ingestion), death may occur.


Calling your health care provider
If you believe you have been exposed to Paraquat, you should seek medical care immediately.


Avoid exposure to paraquat.

Johns Hopkins patient information

Last revised: December 3, 2012
by Martin A. Harms, 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.