Hydroxychloroquine Side Effects: Risks and Monitoring

Millions of people take hydroxychloroquine (brand name Plaquenil) daily for lupus, rheumatoid arthritis, and other autoimmune conditions. While it is generally considered one of the safer disease-modifying drugs available, long-term use comes with real risks that call for regular monitoring. Understanding hydroxychloroquine side effects — particularly the threat to your eyesight — is critical for anyone taking this medication for months or years. The reassuring part: most serious side effects are preventable or manageable when caught early through the monitoring your care team sets up.

This guide explains what hydroxychloroquine treats, its common and serious side effects, the eye-screening schedule that protects your vision, its interactions, and exactly when to call your doctor or seek emergency help. It is general education, not a substitute for your rheumatologist or ophthalmologist.

What Hydroxychloroquine Treats and How It Works

Hydroxychloroquine is an antimalarial drug that has been repurposed for autoimmune diseases. It modulates the immune system by interfering with antigen processing inside immune cells, dampening inflammatory signaling without the broad immunosuppression caused by drugs like prednisone. According to the FDA label, it is approved for malaria prevention and treatment, systemic lupus erythematosus (SLE), and rheumatoid arthritis.

The drug accumulates slowly in body tissues, which is why it can take two to three months to reach its full therapeutic effect. That same gradual buildup explains why some side effects — particularly retinal toxicity — tend to emerge only after prolonged use. Your prescriber sets the dose and adjusts it over time; they base it on factors such as your body weight and kidney function to keep long-term risk as low as possible.

Common Hydroxychloroquine Side Effects

The most frequently reported hydroxychloroquine side effects are gastrointestinal and are generally mild:

• Nausea — one of the more common effects, usually easing after the first few weeks
• Diarrhea
• Abdominal cramps or bloating
• Loss of appetite
• Headache
• Dizziness
• Skin rash or itching
• Hair thinning — usually mild and reversible

According to MedlinePlus, taking hydroxychloroquine with food or milk can reduce stomach upset. Some people find their GI symptoms improve within the first month. Do not change how or when you take the drug on your own — if side effects are bothering you, your prescriber can suggest options such as taking it with food or adjusting the regimen.

Retinal Toxicity — The Most Important Risk

Retinal damage is the most serious long-term concern with hydroxychloroquine. Over time the drug can accumulate in the retina, producing a characteristic pattern of injury sometimes called “bull’s-eye maculopathy.” Once established, this damage can cause permanent, irreversible vision loss. The American Academy of Ophthalmology (AAO) published updated screening recommendations in 2016 that remain the widely used standard.

What raises the risk of retinal toxicity

• Duration of use: Risk is low in the first five years and rises with cumulative years of use, becoming meaningfully higher after 10 to 20 years.
• Dose relative to body weight: AAO guidance recommends keeping the daily dose at or below 5 mg per kilogram of actual body weight to reduce risk. This figure is the ceiling clinicians use when they calculate your prescription — it is guidance for your prescriber, not a dose for you to set or adjust yourself.
• Kidney disease: Impaired kidney function slows clearance and increases exposure.
• Concurrent tamoxifen use: Tamoxifen independently affects the retina and appears to amplify hydroxychloroquine toxicity.
• Pre-existing macular disease: Existing retinal conditions can raise risk and complicate screening.

The eye-screening schedule that protects your vision

The AAO recommends a baseline eye examination within the first year of starting hydroxychloroquine, followed by annual screening beginning after five years of use — or sooner if you have risk factors such as kidney disease, higher dosing, or tamoxifen use. Screening should go beyond a routine vision check: it should include optical coherence tomography (OCT) and automated visual field testing (testing patterns are adjusted for patient background, since the pattern of early damage can differ). Early detection lets your care team act before irreversible damage occurs. Because the damage cannot be reversed once it is established, keeping these appointments is essential for anyone on long-term therapy.

Cardiac Side Effects

Hydroxychloroquine can affect the heart, particularly with long-term use, at high doses, or in overdose. Cardiac effects include:

• QT prolongation — the drug can lengthen the QT interval on an ECG, which can increase the risk of abnormal heart rhythms; this drew heightened attention when the drug was combined with azithromycin during the early COVID-19 period
• Cardiomyopathy — rare but documented with long-term, high-dose therapy; possible signs include shortness of breath, swelling, and reduced exercise tolerance
• Conduction disorders — bundle branch block and other conduction abnormalities have been reported

The Mayo Clinic notes that periodic ECG monitoring may be appropriate for some patients on long-term therapy, especially those with existing heart conditions or those taking other QT-prolonging medications. If you develop unexplained shortness of breath or palpitations, tell your clinician so cardiac evaluation can be considered.

Low Blood Sugar (Hypoglycemia)

Hydroxychloroquine can lower blood glucose, and severe hypoglycemia has been reported even in people who do not have diabetes. If you take insulin or other diabetes medicines, the effect can add up — monitor your glucose as your care team directs, and learn the warning signs of low blood sugar (shakiness, sweating, confusion, rapid heartbeat). Patients also taking a drug like Jardiance should coordinate glucose monitoring with their prescriber.

Drug Interactions

Hydroxychloroquine interacts with several medication classes:

• QT-prolonging drugs — azithromycin, fluoroquinolones, amiodarone, and certain antipsychotics; combining these can increase the risk of dangerous heart rhythms
• Digoxin — hydroxychloroquine can raise digoxin blood levels, risking toxicity
• Insulin and other diabetes medications — the blood-sugar-lowering effect can be enhanced, increasing hypoglycemia risk
• Antacids — aluminum- and magnesium-containing antacids can reduce absorption; separating the doses by several hours is commonly advised
• Tamoxifen — increases retinal toxicity risk, as noted above
• Cyclosporine — levels may rise

Give every prescriber and pharmacist your full medication and supplement list so interactions can be checked. For broader medication-management context, visit our medical conditions guide.

Neurological and Psychiatric Effects

Less commonly, hydroxychloroquine can affect the nervous system. Neuromuscular weakness — particularly proximal muscle weakness in the thighs and upper arms — has been reported with long-term use and is usually reversible after the drug is stopped under medical supervision. Rare psychiatric effects such as anxiety, mood changes, and, very rarely, psychosis have been described. According to the National Institutes of Health, peripheral neuropathy (numbness and tingling in the hands and feet) occurs rarely but may become lasting if not addressed promptly. Report any new numbness, tingling, or muscle weakness to your clinician.

Is Hydroxychloroquine a COVID-19 Treatment?

No. Hydroxychloroquine is not an FDA-authorized or FDA-approved treatment for COVID-19. The FDA issued an emergency use authorization early in the pandemic and then revoked that authorization in June 2020 after data showed it was unlikely to be effective for COVID-19 and raised concerns about serious cardiac side effects. Subsequent large trials did not show a benefit for treating or preventing COVID-19. Take hydroxychloroquine only for a condition your prescriber has prescribed it for, at the dose they set.

Overdose Is Dangerous

Hydroxychloroquine has a narrow margin of safety, meaning the gap between a therapeutic dose and a toxic one is small — overdose can cause life-threatening heart rhythm problems very quickly and is especially dangerous for children. Keep the medication secured and out of reach of children. If you suspect an overdose or accidental ingestion, call the Poison Control hotline at 1-800-222-1222 right away, and call 911 for any collapse, seizure, or severe symptoms.

When to Call Your Doctor

Contact your healthcare provider if you experience any of the following while taking hydroxychloroquine:

• Any change in vision — blurring, difficulty reading, light sensitivity, or missing spots in your visual field
• New muscle weakness, especially difficulty climbing stairs or lifting your arms
• Numbness or tingling in the hands or feet
• Ringing in the ears or changes in hearing
• Symptoms of low blood sugar (shakiness, sweating, confusion)
• Persistent GI symptoms that do not improve
• Unexplained bruising or bleeding
• Mood changes, irritability, or unusual behavior
• Blue-gray discoloration of the skin, nails, or the inside of the mouth

Seek emergency care (call 911 or go to the nearest emergency room) for chest pain, a severe or irregular heartbeat, fainting, sudden vision loss, or signs of a severe allergic reaction. Skin pigmentation changes — a blue-gray discoloration of the skin (often the shins and forearms), nails, and mucous membranes — are an under-recognized long-term effect; they are usually harmless and may partially fade after the drug is stopped, but report them so your clinician can confirm.

Frequently Asked Questions

How often should I get my eyes checked while on hydroxychloroquine?

The American Academy of Ophthalmology recommends a baseline exam within the first year, then annual screening starting at five years of use. If you have risk factors (kidney disease, higher dosing, tamoxifen use), annual screening should begin sooner. These exams should include OCT and automated visual field testing, not just a routine vision check.

Does hydroxychloroquine cause weight gain?

Weight gain is not a commonly reported side effect. Some people with autoimmune conditions actually manage their weight better on the drug because reduced inflammation allows more physical activity. Appetite and weight changes are more often linked to the underlying condition than to the medication itself.

Can I take hydroxychloroquine during pregnancy?

Hydroxychloroquine is one of the few disease-modifying antirheumatic drugs generally considered compatible with pregnancy. The American College of Rheumatology’s reproductive-health guidance supports continuing it during pregnancy for many patients with lupus, because stopping can trigger flares that pose greater risks to mother and baby. Always plan pregnancy with your rheumatologist.

How long does it take for hydroxychloroquine to start working?

Most people notice improvement within two to three months, with full effects often taking longer. The slow onset can be frustrating, but the drug’s long-term benefits for disease control are well established. Your doctor may use short-term bridging therapy while you wait for it to take effect.

Is hydroxychloroquine safe to take for COVID-19?

It is not an authorized COVID-19 treatment. The FDA revoked its emergency use authorization in June 2020, and later studies did not show a benefit. Use it only for the condition your prescriber has prescribed it for.

Sources

• American Academy of Ophthalmology — 2016 recommendations on screening for chloroquine/hydroxychloroquine retinopathy
• MedlinePlus — hydroxychloroquine drug information
• FDA — drug label and June 2020 revocation of the COVID-19 emergency use authorization
• American College of Rheumatology — reproductive-health and DMARD guidance
• Mayo Clinic — hydroxychloroquine precautions and monitoring
• National Institutes of Health — neuromuscular and neuropathic effects