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Chloroquine and Hydroxychloroquine Can Have Serious Side Effects

The Bottom Line

Two old drugs used for malaria, chloroquine and hydroxychloroquine, are being studied for their potential to treat coronavirus disease of 2019 (COVID-19). Side effects from these drugs can be very serious and include irregular heart rhythms that can result in death. Check state COVID-19 website resources and telephone hotlines for more information about COVID-19 in your area.

The Full Story

In response to COVID-19, healthcare providers and scientists around the world are trying to find treatments. It has been suggested that chloroquine and hydroxychloroquine might be effective additions to treatment of COVID-19 in some patients. These drugs have been used for decades for malaria and, more recently, for some types of arthritis. Their possible use for COVID-19 is based on experience from the Severe Acute Respiratory Syndrome (SARS) outbreak of 2003 (also caused by a coronavirus), expert opinion, in-vitro observations (in the test tube, not people), and early results of clinical trials currently taking place in hospitalized patients. Despite recent public endorsements, the use of these medications for treatment of COVID-19 is still experimental, and they should not be used without close monitoring by a physician in one of these trials. It might turn out that neither of these medicines effectively treats or prevents COVID-19.

When a virus infects cells in your body, it tricks the cells into using their own machinery to make copies of the virus instead of doing all the things your cells would normally do to keep you alive and healthy. The COVID-19 virus targets cells in the lungs. Infected lung cells start creating a huge number of copies of the COVID-19 virus. Eventually the cells are overwhelmed and die. The dead cells burst, and the many copies of the virus are released. Those copies of the virus infect more lung cells, and the process repeats itself.

The unprecedented spread and severity of COVID-19 has left everyone trying to rapidly adapt. Scientists and physicians are testing chloroquine and hydroxychloroquine to see if these medications might benefit patients who are seriously ill from COVID-19. There is a long safety and effectiveness assessment process that a new drug has to go through before it can be used to treat human illness. Medications like chloroquine or hydroxychloroquine that are approved to treat other human illnesses have already been through the FDA approval process for those other uses, and their safety profiles have been established. The time to approval for a new use could be greatly reduced if they are found to be effective in treating COVID-19. However, it is important to remember that we are still in the experimental phase, and these medications should not be used at home to treat or prevent COVID-19.  

Chloroquine and hydroxychloroquine are currently being given to some confirmed positive, hospitalized COVID-19 patients who have severe symptoms plus one or more risk factors. These critically ill patients might already be on a ventilator to assist breathing. They have been evaluated to make sure they have no pre-existing medical conditions that would exclude them from taking the drugs. Once the patient is approved, the drugs are dispensed from the Strategic National Stockpile. Patients are connected to continuous heart monitors and also get serial electrocardiograms (electrical monitoring of the heart) to look for abnormal heart rhythms before they become life-threatening. Some people have had to be taken off chloroquine or hydroxychloroquine therapies because the healthcare team found that they were developing one of these dangerous heart rhythms. Additionally, a patient who is sedated and on a ventilator cannot be assessed for other serious side effects of the drugs, such as changes in vision and hearing, neuropsychiatric events, and intense nausea.

Chloroquine and hydroxychloroquine have major drug interactions with other medicines that can put a person at an even greater risk of an abnormal heart rhythm. For example, a commonly used antibiotic, azithromycin, is also being investigated for a possible benefit in treating COVID-19, but it has a known major drug interaction with chloroquine and hydroxychloroquine. Whenever a new drug is to be added, the risk versus benefit of a person's existing therapy must be re-evaluated. In some cases, usual medications can be stopped temporarily, and chloroquine or hydroxychloroquine could be started. In other cases, it would be harmful to stop usual medications, and chloroquine or hydroxychloroquine could not be used. Each situation is different and has to be decided on a case-by-case basis.

This is a rapidly evolving subject and there will no doubt be more information and misinformation coming. If you have questions, talk to a trusted healthcare provider or contact Poison Control.

If someone has taken chloroquine or hydroxychloroquine, use the webPOISONCONTROL® online tool for guidance or call Poison Control at 1-800-222-1222. 

For More Information

If you are sick or caring for someone. Atlanta: Centers for Disease Control and Prevention; 2020 Mar 13 [cited 2020 Mar 29].

Prevent getting sick. Atlanta: Centers for Disease Control and Prevention; 2020 Mar 27 [cited 2020 Mar 29].

COVID-19 (SARS-CoV-2, Coronavirus) Information Resources by State


A man thought aquarium cleaner with the same name as the anti-viral drug chloroquine would prevent coronavirus. It killed him. Washington Post (Online) 2020 Mar 24 [cited 2020 Mar 29].

Cortegiani A, Ingoglia G, Ippolito M, Giarratano A, Einav S. A systematic review on the efficacy and safety of chloroquine for the treatment of COVID-19. J Crit Care. 2020 Mar 10.

Devaux CA, Rolain J-M, Colson P, Raoult D. New insights on the antiviral effects of chloroquine against coronavirus: what to expect for COVID-19? Int J Antimicrob Agents. 2020 Mar 11:105938.

Edwards E, Hillyard V. Man dies after taking chloroquine in an attempt to prevent coronavirus. 2020 Mar 23 [cited 2020 Mar 29].

Information for clinicians on therapeutic options for COVID-19 patients. Atlanta: Centers for Disease Control and Prevention; 2020 Mar 21 [cited 2020 Mar 29].

Lexicomp, Lexi-Drugs Online, Chloroquine and Hydroxychloroquine – Adverse Reactions.  Hudson, Ohio: Wolters Kluwer Clinical Drug Information, Inc; 2020; Updated 3/28/2020. Accessed 3/29/2020.

Liu J, Cao R, Xu M, et al. Hydroxychloroquine, a less toxic derivative of chloroquine, is effective in inhibiting SARS-CoV-2 infection in vitro. Cell Discov. 2020;6(1):16.

Medical experts explain the use and potential adverse effects of chloroquine and hydroxychloroquine for COVID-19. Phoenix: American College of Clinical Toxicology; 2020 Mar 25 [cited 2020 Mar 27].

Savarino A, Di Trani L, Donatelli I, Cauda R, Cassone A. New insights into the antiviral effects of chloroquine. Lancet Infect Dis. 2006 Feb;6(2):67-9.


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Prevention Tips

  • Never take any medication without first consulting your healthcare providers.
  • Chloroquine and hydroxychloroquine interact with many other medications. Ask your pharmacist about potential drug interactions between all your prescription, over-the-counter, and herbal medications.
  • Only obtain COVID-19 information from trusted sources, such as the Centers for Disease Control (CDC) website, the World Health Organization (WHO) website, and Poison Control.

This Really Happened

A husband and wife saw a press release about the promise of chloroquine for treatment of COVID-19. They recalled that chloroquine was in the treatment that they use for their fish pond. Even though neither of them had symptoms of COVID-19 and had no history of being exposed to people with COVID-19, they both took unknown quantities of this chemical, and both became very ill with symptoms of fever, vomiting, dizziness, difficulty breathing, and falling down when trying to stand. They were transported to a hospital where the husband died of chloroquine poisoning. The wife survived.

In an interview after this tragedy, the wife urged the public to talk to their doctors and not try to treat themselves. She reported that she and her husband were otherwise healthy but afraid of getting sick with COVID-19. Their decision to try to use this fish pond treatment as a medication led to a death.