An inverse association between the TIII and MPOWER measures and a positive association between the TIII and adult daily smoking prevalence was found. The higher the benefit to tobacco industries or the fewer the preventive measures, the lower the country’s MPOWER package implementation. Countries with high tobacco industry interference had a low level of tobacco hazard warning policies or tobacco advertising prohibition policies. Where the tobacco industry received incentives that benefited its business and public officials faced conflicts of interest with tobacco companies, smoking prevalence was high in some countries. There was little effect in females for tobacco industry interference, and most adults daily smoking, but a positive effect was shown among males.

WHO Article 5.3 has guideline recommendations on awareness-raising, limiting interaction with the tobacco industry, rejection of industry partnerships, avoidance of conflicts of interest, transparency, denormalization of industry CSR activities, preferential treatment of the tobacco industry, and state-owned tobacco industries [14]. According to Fooks et al., only 6% of parties have introduced more than half of the requirements of Article 5.3. Moreover, 16% of guideline recommendations have been implemented among parties, implying an extensive opportunity for tobacco industry influence [15]. Parties must remain alert and ensure that Article 5.3 is implemented across different government sectors, aiming at policy coherence that does not favor the tobacco industry’s interests over parties’ obligations under the FCTC [2]. United States of America (USA), who has leading cigarette manufacturing, remains a non-ratified FCTC party [16].

The study results support the previous findings that the tobacco industry’s interference weakens the national tobacco control policy or MPOWER package [17]. Our results confirmed an argument that tobacco companies' strategies interfered with tobacco control policies which might contribute to increasing the smoking prevalence. When the government’s preventive measures against interference in the tobacco industry were insufficient, or when the tobacco industry benefited greatly, the implementation of FCTC and MPOWER scores were lower. In particular, the tobacco industry exerted a powerful force to block the policy of inserting warnings or pictures on tobacco packages or weaken the ban on sponsoring advertisements for tobacco products. This study identifies that several measures protecting tobacco control policies from the commercial and other vested interests of the tobacco industry have not yet completely prevented the tobacco industry from interfering with tobacco control policies [2]. The study results also show higher rates of male smoking in countries where public officials face conflicts of interest, consistent with Article 5.3 guidelines recommending rules for public servants to avoid conflicts of interest for protecting public health policies from interference with the tobacco industry [18]. Legislators have become vulnerable to tobacco business interference by receiving political contributions [19].

The study also found that the greater the tobacco interference, the lower level of warning about the dangers of tobacco which shows tobacco companies use packaging and other advertising techniques to make cigarettes attractive and misrepresent the fact that tobacco products are detrimental to health [20]. In addition, we found that enforcement of bans on TAPS decreased as tobacco business interference increased, contrary to Article 13 of the FCTC. We recommend that all tobacco industry interference with TAPS should be regulated, including direct advertising bans such as mass media, outdoor advertising, point-of-sale (POS) advertising materials, indirect advertising bans inducing brand stretching, brand sharing, and product placement, etc. [21].

This study also supports the previous hypothesis that countries with high tobacco industry interference have more problems with tobacco use or smoking epidemics [22]. The sabotage strategy from the tobacco industry weakens the MPOWER package and national tobacco control level. Our study results showed that tobacco industry’s activities increased the population's tobacco consumption, confirming that the tobacco industry might be a primary facilitator of the tobacco epidemic. Meanwhile, tobacco use can be explained as the tobacco user as a host, the tobacco product as an agent, and policy or media as an environment [23]. Eliminating the tobacco industry’s influence on health policy is vital for effective tobacco control and reducing health risks. The WHO underscores that raising tobacco taxes is the most effective strategy to curb tobacco use [14]. Considering the tobacco industry’s strong opposition to such tax measures, it’s evident that their role in health policy, especially in taxation matters, needs stringent oversight.

The results show that the tobacco industry's influence on the smoking prevalence rate is more significant for males than females. Given the smoking epidemic in women generally lagging behind men by 30–40 years [24], it is expected that smoking among women will increase first among those with higher socioeconomic status, as it did with men several decades prior, and a gap between gender will continue to narrow [25]. Historical women's liberation movements encouraging equal smoking to men might have increased the women’s smoking rate even in the low TIII countries might have nullified existing associations in women subgroup analysis. In this context, tobacco business activities could impact the increase in the smoking rate for both sexes.

One of the most vital indicators of conflict of interest is whether the government owns the tobacco companies through weak tobacco control in SOTCs, such as low tax rates, no indoor smoking restrictions, sales of tobacco products to youth, and loose advertising regulations, etc. [25] Countries in which the government monopolizes the production and sales of tobacco products or owns at least one tobacco company must have a high TIII score based on a conflict of interest [26]. Contrary to expectation, the TIII scores were not significantly higher in SOTCs. Based on economic theory, one possible reason might be that tobacco company monopolies lack competitive incentives to actively engage in sales tactics such as mass advertising and encouraging sales to youth and women. The other possible reason is the small sample size for countries with SOTCs.

Some limitations need to be considered when interpreting the results. First, our findings from the 30 selected countries may not generalize to a wider pool of countries. Second, measurement errors need to be considered. Random measurement error in the exposure variable will bias associations towards the null [27]. Previous studies have used TIII as an exposure variable. In a study that evaluated the degree of FCTC 5.3 implementation in seven Asian countries using the TIII, the scoring system was designed with the help of tobacco control experts and validated through a focused group discussion [28]. Hoe et al. have argued that one of the most cited barriers to tobacco control policy implementation worldwide is tobacco industry interference. At the same time, TIII 2019 showed that adherence to Article 5.3 had been far from satisfactory worldwide [29]. Jeffrey Drope et al. found strong evidence that interference in tobacco control policymaking has increased in some countries in Latin America with the assessment results using the TIII 2020 [30].

Brunei Darussalam's case offers a compelling insight into the complexities of tobacco control. Despite its regulatory solid stance, evidenced by a low score on the Tobacco Industry Interference Index, tobacco consumption has only slightly declined from 16.7% in 2000 to 16.2% in 2020 [31, 32]. This suggests that while regulations are vital, they might need to be more sufficient on their own. A holistic approach, combining regulations with public awareness campaigns, education, and community engagement, is essential for impactful tobacco control. Brunei's experience underscores the importance of ongoing monitoring and adaptable public health strategies. While the FCTC and MPOWER were introduced in 2005, tobacco policies existed long before that date. Countries already had diverse trajectories of smoking prevalence rates prior to the introduction of these initiatives. Our World in Data reveals variations in tobacco use trajectories following the FCTC enactment in 2005. Some countries saw tobacco use rise by over 30%, while others reported a decline of more than 50% [33]. Analyzing countries with increased smoking rates post-FCTC against those with significant declines could provide insights into the effectiveness of different TIII scores and broader influences on tobacco consumption trends. This comparative analysis can provide valuable insights into effectiveness of different TIII scores and the broader influences on tobacco consumption trends. However, there were too few countries in our data to permit a stratified analysis.

As the national compliance with the FCTC decreased, prevalence rates for adult daily tobacco smokers increased if the tobacco industries’ interference was high. Tobacco industry tactics have been evolving to promote and grow tobacco businesses. Thus, it is crucial to resist tobacco industry disturbances to protect public health and save lives from harmful tobacco use. Governments and global society should counter tobacco industry interference to protect public health and advance tobacco control policies.