In the light of the results obtained it was possible to deduce that the trends obtained from search engines can be a tool capable of monitoring the information needs of the public in real time. In this context, Anderegg & Goldsmith [24] already stated that GT was a tool recognised as a solid and valid indicator for predicting information search behaviour patterns. Jankowski & Hoffmann [25], noted that the data resulting from Google searches could be a valuable source of information for assessing the popularity of medications and the harm they cause and can even help to monitor trends in their consumption.

However, Johnson & Mehta [26] pointed out that the data being analysed are ecological and the findings might not be representative at an individual level. For example, the trends are population-based and one cannot conclude that the entire search volume is generated by individuals with drug-related problems. It is therefore important to note that the value of the RSV analysis for the proposed topics was to find out what users all over the world searched for in a particular period of time and to see how social behaviour developed.

An issue that must be made clear is that at the time when the searches were performed the topic “drug-related problem” did not exist. Consequently, the general public, like researchers, used a range of terms to locate information on the undesirable effects of medicines. This inconvenience, as already mentioned in the introduction to this article, would explain the search for a terminological consensus [1,2,3].

The higher result obtained for drug overdose may be due to the fact that a good many searches associated with suicide [27] or narcotic abuse [28] were being retrieved under this term. This is confirmed if the related queries prominently including searches on “opioid overdose” are considered. On the other hand, with “contraindication” the existence of studies related to self-medication [29] or treatment review [30] was observed. In other words, these terms are extensively used, but do not always represent the same concept.

In the comparative breakdown of the global results by country, the predominance of each topic in a particular region was clear. Although it is hazardous to associate the results with differences in Internet access between territories [17], a clear difference was observed between the interests of English-speaking countries (the United States, Canada, the United Kingdom, Australia, etc.), where the use of the “drug overdose” topic stands out, and other countries. This unity of terminological practice has already been observed in other previous studies [15, 31].

Perhaps the differences might be based on the different models of drug dispensing in the world [32], the legislative differences regulating this dispensing [33] or the avoidable harm related to medication [34]. In any case, the RSV data obtained with GT show the interest of the population, of various countries, in the subject under consideration. As has been demonstrated in previous studies [15, 35], trend trackers are a tool that can be integrated, in real time, into the monitoring of the population’s health information needs.

The search trends showed increasing values, except for the “medication error” topic, whose linear pattern demonstrated that the public had little interest in this subject or was even unaware of the term. In the case of “drug interaction”, a progressive lack of interest in searches related to this term was observed. Actually, of the five topics studied, these two seem to be more commonly used in the professional sphere: in the case of “medication error”, the public usually interprets it more as an adverse effect [36, 37], and “drug interaction” is a term little known to non-professionals [38] and generally not explained by community pharmacists [39]. Ayala-Aguirre et al. [35], have already pointed out that searches with technical words are not common in GT, and therefore most of the population tends to look for information using words in common use.

On the other hand, the “drug overdose”, “contraindication” and “adverse drug reaction” topics showed similar increases in their RSV. However, attention should be drawn to the exponential pattern presented by “adverse drug reaction”, where the highest growth was experienced from 2019. This situation was interpreted as an increased interest among the general population in adverse reactions caused by medication. It must be borne in mind, as Coleman & Pontefract [40] rightly pointed out, that adverse reactions to medicines are still a challenge for modern medical care, particularly given the growing complexity of treatments, the ageing of the population and the increase in multimorbidity.

It is true that there are differences between countries and languages, as is recognised below in the limitations of this study. Even so, one should take into account that various other factors may also exert an influence. For example, there is the great variety of healthcare systems even within the same continent; in the European Union alone there are a multitude of models with major differences in both organization and legislation [41]. Moreover, it is important to note that searches for one of the most searched terms, “drug overdose”, are concentrated in North America, which may be of interest bearing in mind that according to the United Nations Office on Drugs and Crime the United States is the leading country for consumption of illicit drugs such as cocaine, amphetamines and opioids [42].

In the study of milestones, a major peak stands out, with a maximum value in July 2018, related to the “drug overdose” topic. This conspicuous event coincides with the date when the singer Demi Lovato was hospitalized, allegedly for a heroin overdose [43], which aroused significant public interest. This observation would reinforce the idea that searches related to narcotics abuse were also being retrieved under this topic [28], though it would confirm that the incidence of milestones may be due to the appearance of news stories related to famous people or in response to specific publicity campaigns resulting in increased interest in searching for information [44].

Likewise, external factors such as epidemics that promote searches for pharmacological treatment or the need for a vaccine can influence search trends, as has been proven in the recent COVID-19 pandemic [20, 21]. On the other hand, pharmaceutical manufacturers may promote prescription drugs in the following countries only: Canada, New Zealand and United States (pharmaceutical manufacturers may not promote prescription opioid painkillers). Pharmaceutical manufacturers can promote over-the-counter medicines in a wide number of countries (searches for over-the-counter medicines were more likely to lead to commercial domains) [19]. This circumstance will also influence an increase in search trends favoured by this advertising.

The milestone trend analysis, or MTA, is a method of tracking progress in project planning. MTA charts can help research team leaders assess the health of a project and provide valuable insights about scheduling or scope for future initiatives [45].

The increases observed in the “adverse drug reaction”, July 2021, and “contraindication”, June 2021, topics could be due to the increase in DRPs caused by the COVID-19 pandemic, since there is research reflecting this [41, 46]. In the case of “drug interaction” and “medication error”, the absence of notable milestones would imply that the population has not seen any reason to perform more searches on them.

In this study seasonality was analysed as fluctuating demand for information on the topics over the course of the year. It was found that although this was present to a moderate degree in “adverse drug reaction”, “contraindication” and “drug interaction”, no very noteworthy data were obtained and they could be due to a wide range of causes. Consequently, in line with the study by Kardeş [42], more research is required to clarify the mechanisms governing this seasonality.

Seasonality is the systematic, though not necessarily regular, movement that occurs in the variables studied over the course of the year, due to changes in the characteristics of the various calendar periods. It is important to study it, as the results may influence decision-making [47] or even the implementation of preventive measures related to specific healthcare problems [48].

The existence of epidemiological behaviour in the information searches under study was not confirmed, since no sawtooth pattern at constant time intervals was observed in its graphic progression, as occurs in other health-related subjects [9]. These results rule out the possibility that the searches analysed behave in a regular fashion related to the time of year. In any case, the graphic pattern of the search trends is a visual means that enables us to recognize the connection between the alternating sections of dialogue in a colloquial conversation (whether verbal, written or digital) and provides a strong cause-effect relationship between the events studied and the need for more information [49].

When analysing the relationship between the various topics, the very strong relationship between “adverse drug reaction” and “contraindication” must be emphasized. The association may be due to the population searching for DRPs without having a clear idea of the difference between one term and another [50], though this confusion may result from the lack of clear information from the health authorities [51], which would represent a clear argument for greater international harmonization of DRPs. There is still an obvious need to adopt a term that will clearly identify the negative results associated with the use of medications and distinguish them from other process elements [52].

However, the divergence in behaviour between the most searched topics (“drug overdose”, “contraindication” and “adverse drug reaction”) and those that aroused less public interest (“medication error” and “drug interaction”) is clear. Perhaps, as has already been suggested, it is because the latter two terms are more specialized and therefore less often used by the general population.

It is important to note that this study did not aim to determine the real results of DRPs. The value of the RSV analysis for the proposed topics lay in finding out what user searches were performed, worldwide, in a particular time period and to see how social behaviour evolves.

Furthermore, the reasons for searching for the various topics may not always be the same, nor can it necessarily be assumed that they will all be searched for in a single operation. This research study was based on Google and did not consider other search engines. However, Google headed the ranking of search engines with the highest number of users in both 2021 and 2022, with a worldwide market share of over 92% [53].

An important point is that GT provides relative values, but not absolute frequencies (total number of searches), which reduces the scope for more real prognosis and statistical analyses. Moreover, greater transparency would be desirable, since there is no information on the specific methods that Google uses to forecast trends; these have not been divulged by the company [54].

In addition, the lack of data regarding the geographic location of the users is a limitation in interpreting engagement.

It is accepted that the searches carried out will not include those carried out with unusual terms, words used in slang and those searches carried out with typographical errors.

Furthermore, it must be borne in mind that Google uses context to improve the results. Some examples of context are location (the most significant results for a particular search may condition how people search), language (results will be positioned depending on the language in which the search is performed), type of device (results are displayed according to the type of screen, distinguishing, for example, between mobile devices and computers) and related results.

Although “big data” such as that collected by GT may be of much value, it should be interpreted with caution as it is not possible to accurately define the population contributing to the data sample. One cannot be sure whether an individual is seeking information because they have the problem or just out of curiosity [55].

Finally, it must be acknowledged that this study is limited to the “connected world”, and there will therefore be a bias regarding the results that can be derived from the behavioural patterns of the population. Moreover, as Cervellin et al. suggest [22], the results obtained with this tool may be influenced by media coverage.

The greatest public interest was found in the drug overdose and contraindication topics, and at the same time it was these that showed the largest upward trend, though the seasonality study did not produce any very significant results, nor did it demonstrate epidemiological behaviour in information searches.

The main milestone observed was due to media factors related to the consumption of narcotics.

There was a clear difference in the use of the drug overdose topic in English-speaking countries (the United States, Canada, the United Kingdom, Australia, etc.).

A correlation between the adverse drug reaction and contraindication topics was confirmed.