Researchers led by Cheewon Ahn and Hyunsuk Jeong at The Catholic University of Korea screened 5,527 records from PubMed, Embase, and the Cochrane Library and ultimately included 57 randomized controlled trials from 53 reports, covering 28 distinct siRNA agents and a total of 11,757 participants. The protocol was registered with PROSPERO, and two reviewers independently performed study selection and data extraction, with disagreements resolved by a third reviewer. Only placebo-controlled or treatment-as-usual randomized trials were eligible, deliberately excluding single-arm and open-label studies, because the diseases targeted by siRNAs are often intractable, with high baseline mortality and hospitalization rates that can masquerade as drug toxicity without a proper control group.

The pooled analysis focused on four hard safety outcomes: death, serious adverse events, severe adverse events, and adverse events leading to treatment discontinuation. Compared with controls, siRNA treatment did not increase the risk of death, with a pooled relative risk of 0.77 and a 95 percent confidence interval of 0.62 to 0.95. Severe adverse events were likewise significantly lower in the treatment group, at a relative risk of 0.85 with a confidence interval of 0.76 to 0.95. The risk of serious adverse events was not increased, with a relative risk of 0.94 and a confidence interval of 0.88 to 1.00, and treatment discontinuation due to adverse events showed no significant increase, at a relative risk of 0.86 with a confidence interval of 0.66 to 1.13. Remarkably, statistical heterogeneity across studies was essentially zero for every outcome, with I-squared values of 0 percent, indicating an unusually consistent safety signal across 28 chemically and pharmacologically diverse molecules.

That consistency matters because siRNA therapeutics work through a mechanism fundamentally different from conventional small-molecule drugs. The guide strand of the siRNA binds to the RNA-induced silencing complex, or RISC, triggering RNA interference within the cell to silence a target gene in a sequence-specific manner. Early siRNA agents suffered from rapid degradation in vivo, off-target effects, and immunogenicity, but modern drugs incorporate a phosphorothioate backbone and ribose modifications such as 2′-O-methyl and 2′-fluoro, which enhance resistance to nuclease degradation and reduce immune activation. In silico sequence design minimizes unintended hybridization, and Good Laboratory Practice toxicology studies determine the initial starting dose for human trials.

Delivery technology has been equally transformative. Triantennary N-acetylgalactosamine, or GalNAc, conjugation targets the asialoglycoprotein receptor, which is predominantly expressed on hepatocytes, facilitating uptake through receptor-mediated endocytosis. This enables highly selective delivery to the liver while minimizing drug distribution to other tissues, and GalNAc has become the preferred delivery system for liver-targeting siRNAs. Six of the seven FDA-approved therapeutics use GalNAc conjugation alongside 2′-O-methyl, 2′-fluoro, and phosphorothioate modifications. The subgroup analysis confirmed that GalNAc-based agents showed no increased mortality risk, at a relative risk of 0.79, and non-GalNAc agents also showed no increase, at 0.66, although the authors caution that unfavorable non-GalNAc drugs may have been discontinued before any data were published, introducing potential publication bias.

The most sobering findings come from the discontinued programs. Of the ten studies in the analysis involving terminated drug development, four were halted because of safety concerns. Three of these were stopped because the delivery vehicle, rather than the siRNA molecule itself, caused mortality in non-human primates. The fourth, revusiran, a first-generation GalNAc-siRNA conjugate with so-called standard template chemistry, was terminated after a mortality imbalance of 23 deaths in the treatment group versus 7 in the placebo group by the end of safety follow-up. Revusiran required weekly 500-milligram subcutaneous injections, whereas vutrisiran, which targets the same indication with second-generation enhanced stabilized chemistry, is administered as a 25-milligram injection once every 12 weeks. The structural stability improvements resulted in markedly different drug exposures, and all other approved and most ongoing siRNA agents now use second-generation chemistry, suggesting that improvements in chemical modification and delivery have translated directly into enhanced clinical safety.

Subgroup analyses by disease category, clinical trial phase, and development status reinforced the overall picture. siRNA treatment did not increase the risk of death in either the rare disease subgroup, with a relative risk of 0.76, or the common disease subgroup, at 0.78. Marketed drugs showed no increased mortality, at a relative risk of 0.76, and agents in ongoing development showed a favorable profile, at 0.47, though most of those data come from early-phase trials with smaller cohorts. The discontinued or terminated subgroup showed a risk similar to control, at a relative risk of 1.01. The quality of adverse event reporting was high, with a median McHarm score of 13 out of a possible 15, and 96 percent of reports specified the number of deaths in each study group, lending credibility to the pooled estimates.

The authors also examined whether the adverse events observed in trials fell within the range anticipated by preclinical safety assessments. Toxicities of siRNA drugs can be classified into three broad types: hybridization- and sequence-dependent effects such as off-target silencing, which are managed preclinically through in silico analysis; hybridization- and sequence-independent effects that occur when plasma concentrations exceed a threshold, which are managed by adjusting dosage and frequency; and hybridization-independent but sequence-dependent effects, including proinflammatory reactions and toxicity to high-exposure organs such as the liver and kidneys. Injection site reactions were the most frequently reported adverse event in the included trials, but the vast majority were mild to moderate and resolved without intervention. Laboratory abnormalities, such as transient liver enzyme or creatinine elevations, were largely not clinically relevant or resolved spontaneously, implying that the adverse events reported in clinical trials generally fell within the anticipated range of preclinical toxicities.

Nevertheless, the researchers emphasize that the reassuring short-term profile does not preclude toxicity in individual patients. Some trials reported serious hepatic or electrocardiogram abnormalities that led to participant withdrawal, and even rare cases where a causal link cannot be excluded underscore the need for rigorous monitoring. The analysis also has limitations: only three trials had follow-up of two years or more, safety was often a secondary endpoint and severe adverse events were not explicitly reported in 24 of the 53 reports, and the study could not evaluate all pharmacological variables, such as dosing schedules or distinct non-GalNAc delivery systems like lipid nanoparticles. Long-term safety will need to be tracked in open-label extension phases, and a five-year extension study of inclisiran found no new safety signals.

For a field that has moved from laboratory curiosity to approved medicine in barely two decades, the meta-analysis represents a milestone: the first systematic quantitative evaluation of key safety outcomes across the entire clinical siRNA portfolio. The findings support the conclusion that chemical modifications and delivery advancements introduced to reduce the toxicity of early-generation siRNAs have successfully translated into enhanced clinical safety. But the authors are careful to note that unforeseen safety issues can still manifest during clinical development, and that thorough safety validation throughout early trial phases, along with extended surveillance for delayed toxicities, remains essential to elucidate the long-term safety profile of these gene-silencing medicines.

Subject of Research: Safety profile of small interfering RNA therapeutics: a systematic review and meta-analysis of randomized controlled trials

Article Title: Safety profile of small interfering RNA therapeutics: a systematic review and meta-analysis of randomized controlled trials

Article References: Ahn, C., Jeong, H., Yim, H. W., Kim, N. J., Han, S., & Oh, I. (2026). Safety profile of small interfering RNA therapeutics: a systematic review and meta-analysis of randomized controlled trials. Frontiers in Drug Safety and Regulation, 6, Article 1855572. https://doi.org/10.3389/fdsfr.2026.1855572

Image Credits: AI Generated

DOI: 10.3389/fdsfr.2026.1855572

Keywords: Safety, profile, small, interfering, therapeutics, systematic, review, meta-analysis, randomized, controlled, trials, scientific research