Substances That Can Harm Your Kidneys (Including a Fruit Most People Don't Expect)

Star fruit — Averrhoa carambola — is a common sight in Southeast Asian markets and home gardens, prized for its tart, refreshing taste. It’s also, according to a body of published case reports, capable of causing severe and sometimes fatal poisoning in people with reduced kidney function. It’s a genuinely surprising entry on a list of nephrotoxic substances, and a useful reminder that “natural” and “safe” aren’t always the same thing when kidney function is compromised.

The star fruit case reports

Multiple published case series describe toxic reactions to star fruit specifically in patients with chronic kidney disease and those on dialysis for end-stage renal failure. The reported symptoms are primarily neurological rather than what you might expect from a food-related reaction: hiccoughing, vomiting, weakness (asthenia), abnormal movement patterns (paresis), muscle twitching, insomnia, mental confusion, convulsions, and in severe cases, coma. Outcomes have in some cases been fatal despite treatment with hemodialysis. Case reports on this have appeared in Clinical Toxicology (2005), the International Medical Journal (2003), and BMC Research Notes (2015) — the latter documenting cases of both acute kidney injury and chronic kidney disease attributed to star fruit intoxication.

The mechanism is thought to involve calcium oxalate crystals — star fruit is notably high in oxalate — causing tubular obstruction within the kidney, alongside a degree of cell death (apoptosis) in the kidney’s tubular epithelial cells. Because a healthy kidney can typically clear excess oxalate without incident, this toxicity is specific to people whose kidney function is already reduced; it isn’t a concern for the general population eating star fruit in ordinary amounts. But for anyone with diagnosed CKD or on dialysis, it’s a genuinely important food to be aware of and typically to avoid.

More familiar nephrotoxic substances

Star fruit aside, a range of more commonly discussed substances carry documented kidney risk, particularly with frequent or heavy use:

NSAIDs (nonsteroidal anti-inflammatory drugs), such as ibuprofen and naproxen, can damage the kidneys if taken in excess at once or too frequently over time. This is one of the more common medication-related kidney risks precisely because NSAIDs are widely available without a prescription and easy to take more often than intended for chronic pain.

Proton pump inhibitors (PPIs), commonly used for ulcers or reflux (GERD), have been associated with an increased likelihood of developing chronic kidney disease when used for extended periods — a less well-known risk given how routinely these medications are prescribed and used long-term.

Certain antibiotics can damage the kidneys if used too frequently, and this can occur even in people with otherwise healthy kidneys, though the effect is more serious in someone whose kidney function is already reduced.

Cisplatin, a chemotherapy drug used as a first-line treatment against various solid tumour cancers, has nephrotoxicity as one of its recognised main adverse effects — a known trade-off that oncology teams monitor closely during treatment.

Environmental and lifestyle exposures

Beyond medications, several other exposures are recognised as nephrotoxic:

• Agricultural chemicals — herbicides and pesticides
• Alcohol
• Smoking (specifically, nicotine)
• Heavy metals — including lead and cadmium

These exposures tend to act more gradually than an acute poisoning event, contributing to kidney risk over years rather than producing an immediate reaction.

What this means practically

None of this is a reason to avoid all of these substances entirely in every circumstance — NSAIDs, PPIs, antibiotics, and chemotherapy all have legitimate, sometimes essential medical uses, and the practical guidance from prevention-focused clinical sources centres on moderation and monitoring rather than blanket avoidance: limiting NSAID use where possible, being cautious with certain antibiotics and the contrast dyes used in some imaging procedures, and having regular blood and urine tests to monitor kidney function, especially for anyone who already has risk factors for kidney disease. Star fruit is the clearer outlier here — for people with diagnosed CKD or on dialysis, the case-report evidence suggests it’s worth avoiding altogether rather than simply moderating.

Frequently asked questions

Is star fruit dangerous for everyone? No — the documented toxicity is specific to people with reduced kidney function, particularly those with chronic kidney disease or on dialysis. The published case reports don’t suggest a risk for people with normal, healthy kidney function eating star fruit in typical amounts.

Are occasional NSAIDs like ibuprofen safe for kidney health? Occasional, appropriately dosed use is generally considered lower risk than frequent or excessive use, but anyone with existing kidney impairment or major risk factors should check with a doctor before regular NSAID use, since the kidney risk is specifically tied to how often and how much is taken.

Why does star fruit affect the kidneys specifically? Star fruit is high in oxalate, and the leading explanation in the case-report literature is that calcium oxalate crystals cause obstruction within the kidney’s tubules, combined with a degree of cell death in the tubular lining — a mechanism that a healthy kidney can generally clear without issue, but a compromised one cannot.

This article is for general information only and does not constitute medical advice. If you have chronic kidney disease or are on dialysis, consult your doctor or renal dietitian about specific foods, medications, and substances to avoid.