NSAIDs raise kidney-injury risk modestly — but sharply in a few specific situations

Non-steroidal anti-inflammatory drugs — ibuprofen, naproxen, diclofenac and the rest — are harder on the kidneys than a paracetamol, but for a healthy person taking them occasionally the increase in risk is modest rather than catastrophic: current use was associated with roughly a 73% higher odds of acute kidney injury across population studies [s1]. The danger concentrates in specific situations, and the clearest of those is combining an NSAID with two blood-pressure medicines at once [s2].

What the pooled evidence shows

A systematic review and meta-analysis in BMC Nephrology gathered population-based observational studies measuring acute kidney injury (AKI) in people taking NSAIDs [s1]. Across ten studies in the general population, the pooled odds ratio for AKI with current NSAID exposure was 1.73 (95% confidence interval 1.44 to 2.07) [s1]. The risk was higher in older people, with an odds ratio of 2.51 (1.52 to 2.68), and among people who already had chronic kidney disease the pooled odds ratio was 1.63 (1.22 to 2.19), with individual studies ranging from 1.12 to as high as 5.25 [s1].

The single most important caveat is about absolute risk. None of the studies reported the baseline rate of AKI in the populations studied, so the review could not translate these odds ratios into an absolute chance of harm [s1]. An odds ratio of 1.73 raises very different things depending on the starting risk — and the authors note that baseline risk, and therefore the absolute risk from NSAIDs, is likely higher in people with CKD and in older people [s1]. That is why the same pill is a different proposition for a healthy 30-year-old and for a 75-year-old with reduced kidney function.

The wide spread among people who already have kidney disease underlines the point: individual studies put the odds ratio anywhere from 1.12 to 5.25, a range too broad to collapse into a single reassuring or alarming number [s1]. It is worth being precise about what these studies measured, too. The exposure was "current use" of NSAIDs, not specifically chronic high-dose use, and the outcome was acute kidney injury — a sudden, often reversible drop in function — rather than the slow development of chronic kidney disease [s1]. The evidence base the review assembled is observational, and the authors are explicit that large studies estimating the absolute risk of harm, using modern definitions of kidney injury, are still needed [s1].

The combination that matters most

The sharpest signal comes from how NSAIDs interact with common blood-pressure drugs. A large BMJ nested case-control study followed 487,372 users of antihypertensive drugs for a mean of 5.9 years, during which 2,215 cases of acute kidney injury occurred, an incidence of about 7 per 10,000 person-years [s2].

Adding an NSAID to a single class of blood-pressure drug — a diuretic, an ACE inhibitor, or an angiotensin receptor blocker — was not associated with an increased rate of AKI [s2]. But the "triple whammy" — an NSAID on top of two of those antihypertensive classes together — was, with a rate ratio of 1.31 (95% confidence interval 1.12 to 1.53) [s2]. And the risk was front-loaded: it was highest in the first 30 days of use, with a rate ratio of 1.82 (1.35 to 2.46) [s2].

The contrast between the double and triple combinations is the useful finding. It suggests the danger is not simply "NSAID plus a blood-pressure drug" but the specific stacking of two blood-pressure drugs from different classes with an NSAID on top, and that the vulnerable window is the beginning of that combination rather than steady long-term use [s2]. The mechanism is plausible — each drug affects a different lever of the kidney's blood flow and fluid balance — but the practical signal from the data is about a combination and a timing, not the NSAID alone.

What this leaves a reader with

The evidence does not say NSAIDs are safe for the kidneys, nor that a normal short course wrecks a healthy person's kidneys. It says the relative risk is modest and the absolute risk depends heavily on who is taking them — older age and existing kidney disease raise the stakes — and that the genuinely high-risk scenario is layering an NSAID onto two blood-pressure drugs, especially in the first month [s1] [s2]. Because that depends on a person's other medicines and kidney function, it is precisely the kind of decision to check with a clinician or pharmacist rather than judge from a headline number.

This article is informational and is not medical advice.

Sources

• Non-steroidal anti-inflammatory drug induced acute kidney injury in the community dwelling general population and people with chronic kidney disease: systematic review and meta-analysis — BMC Nephrology, 2017-08-01
• Concurrent use of diuretics, angiotensin converting enzyme inhibitors, and angiotensin receptor blockers with non-steroidal anti-inflammatory drugs and risk of acute kidney injury: nested case-control study — BMJ, 2013-01-08