Hydroxychloroquine Side Effects

Hydroxychloroquine (brand name Plaquenil) side effects range from more common, mild issues such as headache, nausea and stomach pain to serious but rare conditions such as heart problems, muscle weakness and convulsions. Side effect risk may increase with higher doses and long-term treatment.

Last Modified: September 5, 2023
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From 1970 to Dec. 31, 2019, there were 24,728 adverse events reported to the U.S. Food and Drug Administration’s Adverse Event Reporting System (FAERS) for hydroxychloroquine, hydroxychloroquine sulfate and Plaquenil.

Of those cases, 20,713 were serious, including 914 deaths. The FDA received nearly half of the reports (9,561) in 2019.

This data has limitations because reports are voluntary, and the FDA cannot verify if hydroxychloroquine caused these side effects. The agency also says most side effects are underreported.

How Common Are Plaquenil Side Effects?

According to the Centers for Disease Control and Prevention, hydroxychloroquine is “a relatively well-tolerated medicine.” The most common, mild side effects such as nausea, stomach pain, headache and vomiting may be lessened by taking the drug with food, the agency said. Taking the drug with milk can also help.

Most side effects will go away after a patient’s body gets used to the medication, according to Brigham and Women’s Hospital.

Some side effects, such as eye damage, are dose dependent. This means the risk goes up with the amount of medicine a person is taking and with long-term use.

The U.S. drug label doesn’t provide any information about how common side effects are because of limited clinical trial data. Plaquenil’s Canadian monograph includes more information on side effect frequency.

Plaquenil’s most common side effects are nausea, stomach pain, headache and vomiting. These may be made less severe by taking the medicine with food or milk.

According to the Canadian monograph, very common side effects occur in more than 10 percent of people. Common side effects occur in one percent to less than 10 percent of people. Uncommon side effects occur in 0.1 percent to less than one percent of people.

Rare side effects occur in 0.01 percent to less than 0.1 percent of people. Very rare side effects occur in less than 0.01 percent of people.

This is not a complete list of possible side effects. Talk to your medical provider if you experience any unusual side effects after taking hydroxychloroquine.

Very Common Side Effects

Side effects in this category are mostly mild and not dangerous. The monograph recommends that patients talk to their medical provider only if these are severe.

  • Nausea
  • Stomach pain
  • Stomach cramps

Common Side Effects

These side effects can range from mild to severe, but the monograph recommends that patients report these to a health care provider in all cases.

  • Diarrhea
  • Headache
  • Itchy skin or rash
  • Loss of appetite
  • Nervousness and changes mood
  • Visual Problems (blurred vision, seeing halos around lights, night blindness, difficulty focusing eyes, blind spots and others)
  • Vomiting

Rare Side Effects

These side effects are rare, but the monograph recommends that patients tell their doctor about these problems if they experience them.

  • Dizziness or vertigo
  • Hair bleaching
  • Hair loss on head or other body parts (alopecia)
  • Nerve and muscle problems (numbness, tingling, burning pain, weakness, difficulty walking, tremors)
  • Ringing in the ears or hearing loss
  • Skin color changes

Unknown Frequency Side Effects

Side effects in this category are the most serious, but there is no information on how common they are. For all cases, patients should talk to their medical provider. For some of these reactions, the monograph recommends patients stop taking the drug and get immediate medical help.

This is only a list for reference. Speak to your medical provider for advice if you have concerns about any side effects.

Contact your medical provider if you experience:
  • Increased sensitivity to sunlight or skin rash because of sunlight
  • Loss of consciousness or fainting spells
  • Low blood sugar (hypoglycemia)
  • Muscle weakness
  • Permanent vision damage
  • Psychosis (hallucinations)
  • Signs of anemia (fatigue; extreme tiredness that doesn’t get better with rest; paleness of lips, skin and nail beds)
  • Signs of liver problems (nausea, vomiting, abdominal pain, jaundice, dark urine)
  • Signs of low platelets for clotting (nose bleeds, gum bleeds, mouth bleeds, tiny red spots on skin)
  • Signs of low white blood cells (fever, chills, infections)
Stop medication and seek emergency medical care if you experience:
  • Allergic reactions or angioedema (rash; hives; swelling of the face, lips, tongue or throat; difficulty swallowing or breathing)
  • Heart rhythm disorders (long QT interval, torsade de pointes, heart block, palpitations, abnormal heartbeat, life-threatening irregular heartbeat)
  • Long-lasting nerve, muscle or tendon problems
  • Seizures, convulsions or fits
  • Signs of heart problems (shortness of breath with exercise or at rest; swelling of legs, ankles and feet; irregular heartbeats; chest pain; seizures or fits; dizziness; tiredness)
  • Skin problems such as Drug Rash with Eosinophilia and Systemic Symptoms (DRESS syndrome), Erythema multiforme or Stevens-Johnson syndrome (flu-like fever, rash, red skin, red or purple patches with blisters or crust in the center, pus-filled rash, peeling skin, itching or burning)
  • Sudden shortness of breath

Warnings and Precautions

Hydroxychloroquine may not be safe for people with certain conditions or taking certain medications.

Use with Certain Medications

People taking hydroxychloroquine should tell their medical providers about all drugs, vitamins, and herbal supplements they take, especially acetaminophen, niacin, iron-containing medications or multivitamins, Lanoxin (digoxin), Nydrazid (isoniazid), Rheumatrex (methotrexate) and Rifadin (rifampin), according to the U.S. National Library of Medicine.

There have been rare reports of psychiatric events, including suicidal behavior, in patients taking Plaquenil.

Liver Disease, Psoriasis, Alcoholism and Blood Disorders

Tell your medical provider if you have a history of liver disease, psoriasis, porphyria or other blood disorders. These conditions may get worse while taking hydroxychloroquine and medical providers will decide if the benefits outweigh the risks before prescribing this medication.

Tell your medical provider if you have a history of alcoholism or take drugs that affect the liver. The medication dose may need to be lowered.

People with glucose-6-phosphate dehydrogenase (G-6-PD) deficiency — a condition where red blood cells break down prematurely — should use the drug with caution.

Low Blood Sugar

People who take hydroxychloroquine may experience severe low blood sugar (hypoglycemia) that can cause potentially fatal loss of consciousness. This can happen in people who take diabetes medications as well as people who do not. Get your blood sugar checked if you experience symptoms.

Eye Damage

Long-term use of this drug can cause permanent eye damage. If your medical provider suspects ocular toxicity, they may discontinue the medication. According to Brigham and Women’s Hospital, less than one in 5,000 develops a serious eye problem.

The risk is highest in people who:
  • Take daily doses larger than 6.5 mg per kilogram of body weight
  • Use the drug for longer than five years
  • Have abnormal kidney function
  • Take the drug with other drugs that may worsen the condition, such as tamoxifen citrate
  • Have macular disease

Heart Problems

Some people who have taken this medication have experienced heart problems, including cardiomyopathy and potentially fatal irregular heartbeats.

Medical providers can use an electrocardiogram to check for irregular heartbeats. If the tests are positive for heart irregularities, they will stop medication. To reduce the risk of heart problems, doctors should correct any electrolyte imbalances prior to patients using the drug, according to the drug’s 2022 prescribing information.


Plaquenil has not been studied in enough people ages 65 or over, and researchers don’t know if seniors respond to the drug differently than younger people. The risk of toxic reactions to this drug may be increased in people with low kidney function. Because older people are more likely to have kidney problems, medical providers may adjust the dose and monitor kidney function.


Children are more sensitive to 4-aminoquinoline compounds in hydroxychloroquine. There have been reports of deaths in children who accidentally ingested chloroquine, even in small doses (0.75 g or 1 g in one 3-year-old child). Hydroxychloroquine should be kept out of reach of children.

Researchers have not studied the safety and effectiveness of Plaquenil in children with systemic lupus erythematosus and juvenile idiopathic arthritis.

Pregnant and Nursing Women

Women should tell their medical provider if they are pregnant, plan to be pregnant, become pregnant while taking the drug or plan to breastfeed.

There has been no increased risk of birth defects in babies born to women who took Plaquenil while pregnant. But embryonic deaths and birth defects have occurred in pregnant rats who received large doses of chloroquine.


The body absorbs compounds in hydroxychloroquine very quickly. If a person overdoses, toxicity symptoms may occur within 30 minutes. Plaquenil overdose can be fatal. People who have any symptoms of an overdose need to get medical help immediately.

Overdose symptoms include:
  • Cardiovascular collapse
  • Convulsions
  • Drowsiness
  • Headache
  • Heart rhythm and conduction disorders (including QT prolongation, torsades de pointes, ventricular tachycardia and ventricular fibrillation)
  • Hypokalemia
  • Sudden potentially fatal respiratory and cardiac arrest
  • Visual disturbances

Stopping Plaquenil

People may need to stop taking hydroxychloroquine because of side effects. They should not stop taking the drug on their own without the help of their medical provider. Plaquenil stays in the body for around three months and it may take a while for side effects to go away.

There is no official data regarding hydroxychloroquine or Plaquenil withdrawal symptoms. But some studies have shown that people may have disease flare-ups after stopping treatment.

For example, data from one study by Anna Zezon and colleagues presented at the 2017 American College of Rheumatology Meeting found that seven out of 27 patients suffered mild and moderate flare-ups of disease after stopping treatment.

Of the two patients with moderate flare-ups, one had arthritis, and the second had low blood platelets counts (thrombocytopenia) and high protein counts in urine (proteinuria).

COVID-19 Precautions

Though some medical providers have used hydroxychloroquine as an experimental treatment for the COVID-19 respiratory illness, the drug’s effectiveness and safety as a treatment for COVID-19 have not been proven.

On April 24, 2020, the FDA issued a drug safety communication warning people that they should not use hydroxychloroquine or chloroquine to treat COVID-19 if they are not hospitalized for the disease and under medical supervision. People should also not use these drugs to prevent COVID-19.

The agency linked the drugs to serious adverse events, including QT interval prolongation, ventricular tachycardia, ventricular fibrillation, and in some cases, death.

The FDA stressed that investigation into these drugs is ongoing and they have not been proven safe or effective for COVID-19 treatment. The agency will communicate with the public when more information is available.

Cardiologists from the American Heart Association, American College of Cardiology and Heart Rhythm Society have expressed concerns with using hydroxychloroquine as a potential treatment for COVID-19 because it may cause dangerous heart rhythm problems.

Medical providers have used hydroxychloroquine experimentally in combination with azithromycin — also known as Zithromax. Hydroxychloroquine and azithromycin used individually can cause rare but potentially fatal heart arrhythmias. Given together, the risk could increase, especially in seriously ill patients.

“The urgency of COVID-19 must not diminish the scientific rigor with which we approach COVID-19 treatment. While these medications may work against COVID-19 individually or in combination, we recommend caution with these medications for patients with existing cardiovascular disease,” Dr. Robert A. Harrington, president of the American Heart Association, said in a statement.

On April 8, 2020, the American Heart Association, American College of Cardiology and Heart Rhythm Society published their guidance for health care professionals in the journal Circulation. The major recommendation is to monitor a patient for QT prolongation, a condition where the heart muscle takes longer to recharge during beats.

QT prolongation can lead to torsades de pointes, a serious heart arrhythmia that can lead to sudden death. Medical providers use an electrocardiogram to measure QT intervals (QTc) for QT prolongation.

Recommendations in the guidance include:
  • Monitor patients’ QT intervals with electrocardiograms
  • Patients with baseline QT prolongation (e.g. QTc ≥500 milliseconds (msec)) or those with known congenital long QT syndrome shouldn’t receive hydroxychloroquine and azithromycin
  • If QTc exceeds a present threshold of 500 msec, stop hydroxychloroquine and azithromycin treatment
  • Medical providers may need to minimize contact with critically ill patients with COVID-19 infection, so optimal monitoring may not be possible
  • Patients with hypokalemia (low potassium) and hypomagnesemia (low magnesium) need treatment to correct these conditions
  • Avoid using other drugs that may prolong QTc whenever possible

Please seek the advice of a medical professional before making health care decisions.