Commercial determinants of health, defined as the set of systems, practices and pathways through which commercial actors influence health and equity,1 shape health and equity, with the pharmaceutical industry acting as a major actor through research, education, and clinical practice. Transparent conflict of interest (COI) disclosures are essential to safeguard the independence of science and medical decision-making.2 Industry payments to researchers and other transfers of value (TOV) can introduce bias into the generation and dissemination of evidence.3 Despite their importance, COI reporting often remains incomplete or inaccurate, highlighting ongoing gaps in transparency.4

The accuracy of interest declarations is critical in clinical practice guidelines (CPG), given their influence on clinical decision-making. Several studies have examined the frequency and quality of interest declarations in CPG. A 2019 systematic review5 involving more than 14,000 CPG authors, reported that 45% had at least one COI, and 32% had undisclosed industry payments. However, this study collected data mostly from USA guidelines. Similarly a North-American6 study of 14 hyperlipidemia and diabetes CPG found that 48% of panel members disclosed COI, while 11% of those reporting no interests were subsequently identified as having undisclosed COI. The study also observed a lower prevalence of COI among authors of government-sponsored guidelines, although COI identification relied on indirect methods, such as prior publications and online sources, which may have underestimated industry relationships.

With respect to scientific societies issuing CPG, Campsall et al.7 studied 95 organizations producing 290 CPG, demonstrating that 63% reported industry funding, organizations with stronger transparency policies issued fewer positive recommendations for patented biomedical products. Nevertheless, this study included only guidelines listed in the National Guideline Clearinghouse, limiting its applicability to other scientific societies, and did not assess COI at the individual author level. In Canada, another study reported that 75% of CPG included at least one author with declared financial COI, and in 54% of cases these relationships involved manufacturers of drugs recommended in the guidelines.8 However, the restricted national scope of this analysis limits its generalizability to European contexts.

The aggregate impact on population health from preventive or therapeutic clinical decisions for common health problems is of great magnitude,9,10 hence the relevance of ensuring that CPG are drafted through procedures that guarantee their independence from interests extraneous to population health. It is important to consider that recommendations regarding the use and interpretation of CPG include the question of the potential influence of COI,2,11 and it is known that financial COI are associated with favorable recommendation among guidelines and recommendation documents.12 If information on the quality of these declarations is unavailable, the recommendation is not applicable.

This study analyzes the prevalence of financial COI disclosures and its accuracy, comparing them with the TOV reported by pharmaceutical industry, made by the authors of major CPG in Spain.

We selected 60 CPG that met our eligibility criteria (see Table S1 in online Supplementary Material), comprising 704 individual authors and 810 authorship instances; because some authors contributed to multiple guidelines, all 810 authorships were analyzed.

Regarding COI declarations, as shown in Table 1, more than half of the authorships (53.6%, n=434) included a COI statement, while the remaining cases (46.4%, n=376) had no available declaration. Of the declarations provided, 224 (51.6%) reported no COI, whereas 210 (48.4%) disclosed conflicts prior to the drafting of the CPG. Differences were observed between men and women authors (p=0.007), with men more frequently reporting receipt of payments than women, 30.2% and 20.7%, respectively.

Guideline coordinators declaration of COI was lower than other contributors (79.1% of coordinators did not submit a declaration, compared to 44.6% among the remaining authors). Additionally, four scientific societies did not systematically include COI statements.

Regarding the 704 authors who participated in these CPG, 80.1% (n=564) received payments, amounting to 4788 transactions with a total value of 13,078,785.66 € (median per author: 7544.85 €; IQR: 23,597.20 €).

The accuracy of the COI declarations submitted by authors in the CPG was limited (Table 2). In up to 271 of the authorships (33.4%), no COI declaration was provided despite records indicating that the individual had received payments from pharmaceutical companies. Additionally, 85 authors (10.5%) declared no conflicts despite having received payments, and 74 (9%) disclosed COIs that were of a lower magnitude than those recorded in the official TOV. Only 68 of the authorships (8.4%) included a declaration of no COI that was fully consistent with the financial disclosures on record.

For 186 (22,96%) authorships, only records from the same year or after the publication of the CPG were available (groups 3, 6 and 9 in Table 2). This limits a reliable assessment of the accuracy of the COI declarations submitted by these authors. However, for the remaining 624 (77%) cases, it was possible to distinguish and classify declarations as either reliable (groups 5 and 7) or inaccurate/missing despite prior TOV having been received (groups 1, 4 and 8). A third scenario was also considered, those cases which no payments were recorded, and no COI declaration was provided (group 2). This classification is presented in Table 3.

The findings indicate that only 137 (16.9%) of the COI declarations made by authors of the 60 reviewed CPG can be considered reliable, while over half (53.09%, n=430) were either inaccurate or absent.

Regarding the reliability of COI declarations by author characteristics, it was observed that, for both men and women, unreliable declarations accounted for more than half of the authorships (52.3 and 54.1%, respectively). Although the frequencies in coordination roles were similar, the reliability of COI declarations was lower among guideline coordinators compared to non-coordinators (13.9% vs. 17.1%). With respect to the scientific societies endorsing the CPGs, five societies were identified in which over 75% of the authorships were associated with unreliable COI declarations. In contrast, only the Ministry of Health and the Spanish Society of Pulmonology and Thoracic Surgery demonstrated over 50% reliability in the declarations submitted (Table 4).

This study shows a high prevalence of COI among authors in our sample of Spanish CPG, in many cases (46%) COI were not fully disclosed, and the accuracy of COI statements was very low.

Despite recommendations issued by academic and institutional scientific entities regarding transparency in COI declarations within CPG,2,17 our findings indicate that current practices among authors remain inadequate. This persists despite evidence of financial relationships between the professionals involved in scientific evidence production18,19 and the observation that Spanish scientific societies tend to fail to include COI declarations, even when their collaborations with private companies are documented.20

One issue identified was that nearly half (46.42%) of the authorships included no COI declaration. This finding was also noted in tow national based similar studies, in which the study Redeguías and the letter to the editor by Briones et al.21 showed that information relating to financial COI remains scarcer, suggesting that it could reduce both the reliability and the quality of the guidelines.21,22 Furthermore, among the declaration provided, 1 in 10 was incomplete and another 1 in 10 was underreported. These findings are consistent with the evidenced by two recent systematic reviews carried out in 201923 and, as an extension of that work, in 2021,24 which showed that the pooled proportion of discrepancies at the authorship level approached 93%. In addition, pooled proportion of authors who accurately disclosed COIs did not overcome the 18%. In our study, the frequency was approximately 17%.

This issue does not only affect the sample of authorships analysed. Several studies assessing financial COI have shown that such conflicts are often not disclosed. For example, in a survey of 192 authors of 44 CPG, participants reported that in 42 of the guidelines in which they were involved, no declarations related to financial COI were made or required.25 Norris et al.26 found that 40% of 250 CPG did not include authors disclosure information. Despite regulatory changes and recommendation regarding COI reporting, a 2023 review of 197 CGP revealed that 20% still did not report any COI information.27 Similarly, a study carried out by Mooghali et al.28 examining American clinicians’ authorships, found that over 60% of CPG authorships did not submit any COI declaration.

Overall, the evidence consistently suggests that COI are frequently underreported or omitted and agree on the impact that this lack of transparency can have on credibility and confidence.

Although there is existing guidance urging scientific societies that endorse CPG to adopt internal regulatory policies and for participating professionals to minimize their conflicts in practice,2 COI declaration within CPG endorsed by scientific societies remain limited. In our analysis, only some institutions such as the Ministry of Health did not include unreliable COI disclosures.

The relationship between pharmaceutical and other private interest and scientific societies is evident, largely due to the disparity in funding capacity between public institutions and private biomedical interest.29,30 In Spain, the situation appears similar, transparency regarding COI declarations remains limited. Although several studies have addressed this issue,21,31–33 formal declarations are still uncommon, and some prominent scientific societies continue to lack comprehensive COI transparency.

These findings underscore not only the need for clearer guidance to declare potential COI but also highlight the importance of applying ethical frameworks, such as the GIN principles,34 and evaluation tools, such as the AGREE framework or IGEST, for all guidelines to ensure the clinical quality, integrity, and independence of CPG.

The interaction between pharmaceutical industry, health professionals, and science societies within healthcare ecosystem, and in general the existence of financial bias is an area of growing concern, as such interactions has been associated with questionable prescribing behaviours by health professionals.35 A systematic review conducted by Mitchell et al.36 demonstrated how these interactions influence and undermine the independent therapeutic practice of clinicians. Reducing the financial bias from the institutions, scientific societies and CPGs remains a priority.37

This study has several limitations. Although our selection of professionals and guidelines was comprehensive, it captures only the COI disclosure landscape of individually selected CPG related with some major causes of disease burden in Spain published in 2016,13 potentially omitting relevant guidelines addressing prevalent health issues with undisclosed conflicts. The sample of authors was limited to those involved in nationally applicable guidelines or those endorsed by Spanish scientific societies, excluding other scientific roles. Another limitation was that gender was inferred from full names, introducing possible misclassification in the absence of self-identification.

A relevant limitation during data extraction in this investigation was the public TOV records availability. While some companies publish accessible documents, others limit their publication to the last three years before the actual date, or they provide documents in non-editable formats (images), which prevented automated data processing and required manual identification and extraction of the data. This creates a heterogeneity in our records selection, which is inevitable since we do not count on a centralized COI database such as OpenPayments in USA. Another limitation is the matching process between the authorship disclosure and the industry records, only referenced by full names and not with an accurate identifier, what could have improved our capability to detect every author's name in the documents and subsequently identify more TOV. Nonetheless, our results confirm that a more sensitive selection would only involve lower reliable disclosures rates, as improving all these limitations would only detect higher rates of TOV from authors with very low transparency attitudes.

Accordingly, we experienced a temporal heterogeneity due to our records availability, which makes newer guideline authors more likely to have TOV detected during our investigation, as a bigger number of previous records were studied.

The analysis relied on aggregated TOV from pharmaceutical companies, without differentiating types of payments. Moreover, some CPG focused on conditions managed primarily through surgical or non-pharmacological interventions, which may have affected COI assessment. Finally, the selected companies do not fully represent industry influence but allow us to evaluate properly CPG authors’ COI declaration. Future studies should broaden the scope to include both pharmaceutical and non-pharmaceutical companies, widely selected, to improve COI detection.

This study demonstrates a lack of adequate COI disclosure among Spanish authors of CPG. Considering the potential influence that clinical recommendations provided in guidelines can exert on healthcare professionals’ decision-making and therapeutic prescription, proper, transparent and regularly updated COI disclosures are essential to ensure the independence and integrity of scientific recommendations. Further research is needed to determine the effect of non-declared COI on clinical recommendations and healthcare decision-making.

Some measures seem to be beneficial to safeguard scientific production integrity and transparency. Scientific societies and professionals should strengthen ethical oversight not only in the development of CPG, but also in all areas where expert knowledge is needed. The current system allows individuals to conceal and not declare COIs without facing any real consequences, thereby undermining trust in scientific outputs.

It would be therefore helpful to implement platforms that facilitate the identification of COI among healthcare professionals and scientists, as other countries established. All stakeholders in health ecosystem should commit to providing transparent, reliable and accessible disclosures.

The anonymized database used in this study can be consulted via Mendeley Data, in the following link: https://data.mendeley.com/datasets/xgbhfs629f/1

Ferrán Catalá-López.

The corresponding author, on behalf of the other authors guarantee the accuracy, transparency and honesty of the data and information contained in the study, that no relevant information has been omitted and that all discrepancies between authors have been adequately resolved and described.

I. Hernández-Aguado, S. Martín-Benlloch and S. Morales-Garzón conceived and designed the study. S. Martín-Benlloch, in collaboration with A.M. Martín Fernández-Gallardo, developed the data collection, and S. Martín-Benlloch conducted the data curation and analysis, with methodological support from S. Morales-Garzón. All authors contributed to the interpretation of the results. S. Martín-Benlloch and S. Morales-Garzón drafted the first version of the manuscript. I. Hernández-Aguado and A.M. Martín Fernández-Gallardo critically revised the manuscript. I. Hernández-Aguado provided senior oversight and ensured the quality and integrity of the work. All authors approved the final version for publication and agree to be accountable for all aspects of the work.

None.

None.