## 3 Collection of the Corpus
### Statistics of the Collected Corpus  
We used the UDPipe [44] package to parse the reviews, in order to get sentence segmentation, tokenization and lemmatization. Given this, we calculated that the average number of sentences for the reviews is 10, the average number of tokens is 152 (with a standard deviation of 44) and the average number of lemmas is 95 (standard deviation equals to 23). The type/token ratio (TTR), calculated as the ratio of the unique lemmas in a review to the amount of tokens in it, is 0.64 for all reviews on average. Detailed information about the annotated corpus is presented in Table 7, including:  
1. The number of mentions for every attribute (\"Mentions--Annotated\" column in the table). 2. The number of unique normalized terms that match the mentions, and the number of unique classes from classifiers as described in Section 3.3 that the mentions belong to (\"Mentions--Classification and Normalization\"). 3. The number of words belonging to mentions of the attribute (\"Mentions--Number of words in the mentions\"). 4. The number of reviews containing any mentions of the corresponding attribute (\"Mentions--Reviews Coverage\"). The corpus contains 8236 mentions of drugs corresponding to 226 ATC codes. The 20% most popular ATC codes (by the number of reviews with the corresponding DrugName mentions) include 45 different codes which appear in 2614 reviews (93% of all reviews). \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Entity Type**} & \multicolumn{3}{c}{**Mentions**} \\ \cline{2-4}  & **Annotated** & **Classification and Normalization** & **Num. Words in the Mentions** & **Reviews Coverage** \\ \hline ADR & 1784 & 316 (MedDRA) & 4211 & 628 \\ \hline Medication & 32,994 & & 47,306 & 2799 \\ \hline Drugname & 8236 & 550 (SRD), 226 (ATC) & 9914 & 2793 \\ \hline DrugBrand & 4653 & & 5296 & 1804 \\ \hline Drugform & 5994 & & 6131 & 2193 \\ \hline Drugclass & 3120 & 70 (ATC) & 3277 & 1687 \\ \hline MedMaker & 1715 & & 2423 & 1448 \\ \hline Frequency & 614 & & 2478 & 516 \\ \hline Dosage & 965 & & 2389 & 708 \\ \hline Duration & 1514 & & 3137 & 1194 \\ \hline Route & 3617 & & 7869 & 1737 \\ \hline SourceInfodrug & 2566 & & 4392 & 1579 \\ \hline Disease & 17,332 & & 37,863 & 2712 \\ \hline Diseasename & 4006 & 247 (ICD-10) & 4713 & 1621 \\ \hline Indication & 4606 & 343 (MedDRA) & 7858 & 1784 \\ \hline BNE-Pos & 5613 & & 14,883 & 1764 \\ \hline ADE-Neg & 85 & & 347 & 54 \\ \hline NegatedADE & 2798 & & 9028 & 1104 \\ \hline Worse & 224 & & 1034 & 134 \\ \hline Note & 4517 & & 21,200 & 1876 \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Size characteristics of the collected corpus. Of them, the 20 most popular ATC codes, which were reviewed in more than 50 posts (2511 posts in total), are listed in Figure 2.  
The most popular second-level ATC codes are: L03 \"Immunostimulants\"--662 reviews (which is 23.6% of corpus); J05 \"Antivirals for systemic use\"--508 (18.5%) reviews; N05 \"Psychopletics\"--449 (16.0%); N02 \"Analgesics\"--310 (11.1%); N06 \"Psychoanaleptics\"--294 (10.5%). The most popular drugs among immunostimulants by the reviews count are: Anaferon (144 reviews), Viferon (140) and Grippferon (71). The most popular antivirals for systemic use are the following: Ingavirin (99), Kagocel (71) and Amixin (58). The proportions of reviews about domestic and foreign drugs to the total number of reviews are 44.9% and 39.7%, respectively. The remaining documents (15.4%) contain mentions of multiple drugs, both domestic and foreign, or mentions of drugs for which the annotators were unable to determine the origin. Among the domestic drugs are the following: Anaferon (144 reviews), Viferon (140), Ingavirin (99) and Glycine (98). Examples of mentioned foreign drugs include: Alfubin (93), Amison (55), Antigrippin (51) and Immunal (42).