Hydroxychloroquine side effects: common problems and when to act

Hydroxychloroquine is widely used for lupus, rheumatoid arthritis, and malaria prevention. For most people it’s well tolerated, but a few side effects can be serious. Knowing what to expect and what to report makes the drug much safer. Below I’ll cover the typical mild effects, the dangerous ones to watch for, who’s at higher risk, and simple monitoring steps you can take.

Common and mild side effects

Many people notice mild issues in the first days or weeks. These include stomach upset, nausea, diarrhea, headache, and occasional dizziness. Skin reactions such as mild rash or itching happen too. These problems often improve after your body adjusts. If they don’t ease in a week or two, talk with your prescriber — you might try taking the medicine with food or switching time of day.

Serious risks and what to watch for

1) Eye problems (retinal toxicity). This is the biggest long-term worry. Damage builds slowly and can lead to lasting vision loss. Risk rises with long-term use (often after several years) or high cumulative dose. Report any new blurriness, trouble reading, color changes, or a dark spot in your vision right away. Most doctors recommend a baseline eye exam soon after starting and regular follow-ups—so you catch issues early.

2) Heart effects (QT prolongation and arrhythmias). Hydroxychloroquine can affect the heart’s rhythm, especially if you already have heart disease or take other drugs that lengthen the QT interval (for example some antibiotics and antidepressants). If you feel fast or irregular heartbeat, dizziness, or fainting, seek care immediately. Your provider may order an ECG before or during treatment if you have risk factors.

3) Low blood sugar and nervous-system effects. Rarely, the drug can cause low blood sugar (dangerous for people on diabetes meds) or mood/behavior changes like anxiety, confusion, or hallucinations. If you notice unusual mood shifts, depression, or severe sleep problems, contact your clinician.

4) Blood and liver effects. Rare drops in blood counts or liver enzyme changes can occur. If you get unusual bruising, persistent fever, yellowing of skin/eyes, or dark urine, get evaluated.

Who is at higher risk? Older adults, people with kidney or liver problems, those on high doses or on treatment for many years, and anyone taking other QT-prolonging medicines. Also mention any chronic eye disease to your doctor before starting.

Practical tips: get a baseline eye exam and follow-up schedule, ask for an ECG if you have heart risk factors or take other QT drugs, tell your provider about all medicines (prescription, OTC, supplements), and don’t stop the drug suddenly without medical advice. If you notice worrying symptoms — vision changes, palpitations, fainting, severe rash, or sudden mood swings — contact your provider or emergency care.

Want more details about dosing, interactions, or alternatives? Check with your healthcare team — they can tailor advice to your health history and make safe choices.