diff --git a/R/get-algorithm.R b/R/get-algorithm.R
index 93fcf25..0120012 100644
--- a/R/get-algorithm.R
+++ b/R/get-algorithm.R
@@ -8,11 +8,14 @@
 #' @examples
 #' \dontrun{
 #' get_algorithm_logic("hba1c")
+#' get_algorithm_logic("gld")
 #' }
 get_algorithm_logic <- function(criteria) {
   algorithm |>
     dplyr::filter(.data$name == criteria) |>
     dplyr::pull(.data$logic) |>
     stringr::str_replace_all("AND", "&") |>
-    stringr::str_replace_all("OR", "|")
+    stringr::str_replace_all("OR", "|") |>
+    # regex are defined with '=~', so convert them into a stringr function.
+    stringr::str_replace_all("(.*) \\=\\~ (.*)", "stringr::str_detect(\\1, \\2)")
 }
diff --git a/R/include-gld-purchases.R b/R/include-gld-purchases.R
new file mode 100644
index 0000000..e37b19d
--- /dev/null
+++ b/R/include-gld-purchases.R
@@ -0,0 +1,33 @@
+#' Include only those who have a purchase of a glucose lowering drug (GLD).
+#'
+#' See [algorithm] for the logic used to filter these patients.
+#'
+#' @return The same type as the input data, default as a [tibble::tibble()].
+#' @keywords internal
+#'
+#' @examples
+#' \dontrun{
+#' register_data$lmdb |> include_gld_purchases()
+#' }
+include_gld_purchases <- function(lmdb) {
+  verify_required_variables(lmdb, "lmdb")
+  criteria <- get_algorithm_logic("gld") |>
+    # To convert the string into an R expression.
+    rlang::parse_expr()
+  lmdb |>
+    column_names_to_lower() |>
+    # Use !! to inject the expression into filter.
+    dplyr::filter(!!criteria) |>
+    # Keep only the columns we need.
+    dplyr::select(
+      "pnr",
+      # Change to date to work with later functions.
+      date = "eksd",
+      "atc",
+      "volume",
+      "apk",
+      "indo",
+      "name",
+      "vnr"
+    )
+}
diff --git a/R/include-hba1c.R b/R/include-hba1c.R
index 3180e7b..802acc1 100644
--- a/R/include-hba1c.R
+++ b/R/include-hba1c.R
@@ -15,13 +15,13 @@
 #' }
 include_hba1c <- function(data) {
   verify_required_variables(data, "lab_forsker")
-  hba1c_criteria <- get_algorithm_logic("hba1c") |>
+  criteria <- get_algorithm_logic("hba1c") |>
     # To convert the string into an R expression.
     rlang::parse_expr()
   data |>
     column_names_to_lower() |>
     # Use !! to inject the expression into filter.
-    dplyr::filter(!!hba1c_criteria) |>
+    dplyr::filter(!!criteria) |>
     # Keep only the columns we need.
     dplyr::mutate(
       pnr = .data$patient_cpr,
diff --git a/R/sysdata.rda b/R/sysdata.rda
index e04eb6c..99e839d 100644
Binary files a/R/sysdata.rda and b/R/sysdata.rda differ
diff --git a/_targets/meta/meta b/_targets/meta/meta
index 54603f2..ca5160a 100644
--- a/_targets/meta/meta
+++ b/_targets/meta/meta
@@ -1,25 +1,28 @@
 name|type|data|command|depend|seed|path|time|size|bytes|format|repository|iteration|parent|children|seconds|warnings|error
 .__global__|object|87b8d4f266c27bf4|||||||||||||||
-algorithm|stem|10ca7cf5842c7665|e6ba0f398c6f1faa|60a40402a9fb99aa|-536052671||t19899.4087817699s|9fa82258c19da069|337|rds|local|vector|||0.001||
-algorithm_csv|stem|98f92607dd48318b|72b6696561a29259|2c530c1562a7fbd1|48686226|data-raw/algorithm.csv|t19893.5100784042s|530f140998b50d1c|112|file|local|vector|||0.003||
-algorithm_rda|stem|66f7362503371611|07904a5fa14d0614|9fd483aca6d9122e|-930623318|/home/luke/Documents/organizations/steno-aarhus/osdc/data/algorithm.rda|t19899.4272374029s|a96add13dbb67aa3|376|file|local|vector|||0.01||
+algorithm|stem|40723e52fd2c0786|e6ba0f398c6f1faa|396a620bf28c517b|-536052671||t19984.6357532965s|cfeff01d1edd45fa|355|rds|local|vector|||0.003||
+algorithm_csv|stem|499e7e860784d28e|72b6696561a29259|2c530c1562a7fbd1|48686226|data-raw/algorithm.csv|t19984.6344032286s|06ecd420619ded44|130|file|local|vector|||0.005||
+algorithm_rda|stem|10280eb55316ebbd|07904a5fa14d0614|b947939e3d638088|-930623318|/home/luke/Documents/steno-aarhus/osdc/data/algorithm.rda|t19984.6357559003s|06569f4b2b5547d7|397|file|local|vector|||0.064||
 column_names_to_lower|function|1f9ed89ec76f0ce4|||||||||||||||
 create_algorithm_data|function|721802c40fcbce4e|||||||||||||||
 create_variable_description_data|function|ede086e002225ffb|||||||||||||||
-get_algorithm_logic|function|87ff06f2c9ce0900|||||||||||||||
+get_algorithm_logic|function|0f0fdebe7fb843f9|||||||||||||||
 get_register_abbrev|function|a82c561691b651df|||||||||||||||
 get_required_variables|function|986ccd76798db1ba|||||||||||||||
-include_hba1c|function|e0b1243dd274269a|||||||||||||||
-internal_rda|stem|7d593b3244eb6fb5|76d906cefcbfa41d|cbd1dbe82f00b76b|765355582|/home/luke/Documents/organizations/steno-aarhus/osdc/R/sysdata.rda|t19899.427237588s|f58dd1a2582f84fa|1758|file|local|vector|||0.008||
+include_gld_purchases|function|5c4b4af47e61ff3e|||||||||||||||
+include_hba1c|function|56a5b4012c489ff5|||||||||||||||
+internal_rda|stem|4cefbc8d2053be42|76d906cefcbfa41d|63728ca9f77d87ee|765355582|/home/luke/Documents/steno-aarhus/osdc/R/sysdata.rda|t19984.6357562591s|5fd1d38a27b446ca|1796|file|local|vector|||0.026||
+join_lpr2|function|73dfa05a6f146f76|||||||||||||||
+join_lpr3|function|1690200e83e2d60d|||||||||||||||
 read_algorithm_data|function|ef107d4466f53ae2|||||||||||||||
 read_variable_description_data|function|bac5d03645e8328d|||||||||||||||
 register_as_md_header|function|1b9b0bb62cc1e264|||||||||||||||
 register_data_as_md_table|function|bbdda3785a7bdb63|||||||||||||||
 registers_as_md_table|function|ab56ce7262ba313b|||||||||||||||
-variable_description|stem|6d3dd1f2baa26b82|c2153d67e5651737|a01d9e94aead7bb8|1287048845||t19899.4087817236s|b9834ab70a709536|1311|rds|local|vector|||0.133||
-variable_description_csv|stem|900853341b756f57|2347307fa16d111b|2c530c1562a7fbd1|113481566|data-raw/variable-description.csv|t19845.4834059685s|75bbd1de9a7a9806|4683|file|local|vector|||0.005||
-variable_description_rda|stem|450aefe34ecbfb32|afe48e93eb17b9c8|92ce3d1b47fe163e|-1262878967|/home/luke/Documents/organizations/steno-aarhus/osdc/data/variable_description.rda|t19899.427237264s|5272409a13fc9df9|1550|file|local|vector|||0.058||
+variable_description|stem|1d60446ae54d3249|c2153d67e5651737|a01d9e94aead7bb8|1287048845||t19984.6357532155s|c5e2c6b0e4727be8|1313|rds|local|vector|||0.201||
+variable_description_csv|stem|900853341b756f57|2347307fa16d111b|2c530c1562a7fbd1|113481566|data-raw/variable-description.csv|t19899.5887162511s|75bbd1de9a7a9806|4683|file|local|vector|||0.005||
+variable_description_rda|stem|912e95a27b0cc7a1|afe48e93eb17b9c8|810d0414c7e649b1|-1262878967|/home/luke/Documents/steno-aarhus/osdc/data/variable_description.rda|t19984.6357551018s|8e5879d34632f507|1546|file|local|vector|||0.153||
 variables_as_md_table|function|bf10d1f0df6a170a|||||||||||||||
-verify_required_variables|function|52bf07b827f57531|||||||||||||||
+verify_required_variables|function|070c8fb3014efb9e|||||||||||||||
 write_external_rda|function|c0c90c7048a0d89b|||||||||||||||
 write_internal_rda|function|95b61d841de16e96|||||||||||||||
diff --git a/data-raw/algorithm.csv b/data-raw/algorithm.csv
index fa6cebc..dd9060e 100644
--- a/data-raw/algorithm.csv
+++ b/data-raw/algorithm.csv
@@ -1,3 +1,4 @@
 name,logic
 hba1c,(analysiscode == 'NPU27300' AND value >= 48) OR (analysiscode == 'NPU03835' AND value >= 6.5)
+gld,atc =~ '^A10'
 
diff --git a/data/algorithm.rda b/data/algorithm.rda
index e017789..9f8da15 100644
Binary files a/data/algorithm.rda and b/data/algorithm.rda differ
diff --git a/data/variable_description.rda b/data/variable_description.rda
index 00d3472..5885c2b 100644
Binary files a/data/variable_description.rda and b/data/variable_description.rda differ
diff --git a/man/get_algorithm_logic.Rd b/man/get_algorithm_logic.Rd
index 59c4486..b7ba8a7 100644
--- a/man/get_algorithm_logic.Rd
+++ b/man/get_algorithm_logic.Rd
@@ -18,6 +18,7 @@ Get the criteria algorithmic logic and convert to an R logic condition.
 \examples{
 \dontrun{
 get_algorithm_logic("hba1c")
+get_algorithm_logic("gld")
 }
 }
 \keyword{internal}
diff --git a/man/include_gld_purchases.Rd b/man/include_gld_purchases.Rd
new file mode 100644
index 0000000..b89bbfa
--- /dev/null
+++ b/man/include_gld_purchases.Rd
@@ -0,0 +1,20 @@
+% Generated by roxygen2: do not edit by hand
+% Please edit documentation in R/include-gld-purchases.R
+\name{include_gld_purchases}
+\alias{include_gld_purchases}
+\title{Include only those who have a purchase of a glucose lowering drug (GLD).}
+\usage{
+include_gld_purchases(data)
+}
+\value{
+The same type as the input data, default as a \code{\link[tibble:tibble]{tibble::tibble()}}.
+}
+\description{
+See \link{algorithm} for the logic used to filter these patients.
+}
+\examples{
+\dontrun{
+register_data$lmdb |> include_gld_purchases()
+}
+}
+\keyword{internal}
diff --git a/man/osdc-package.Rd b/man/osdc-package.Rd
index 6c8a49c..8c30eb9 100644
--- a/man/osdc-package.Rd
+++ b/man/osdc-package.Rd
@@ -6,6 +6,8 @@
 \alias{osdc-package}
 \title{osdc: Open Source Diabetes Classifier (OSDC) for Danish Registers}
 \description{
+\if{html}{\figure{logo.png}{options: style='float: right' alt='logo' width='120'}}
+
 This classifier first identifies a population of individuals with any type of diabetes mellitus and then splits this population into T1D and T2D by identifying individuals with T1D and classifying the remainder of the diabetes population as T2D.
 }
 \seealso{
diff --git a/tests/testthat/test-include-gld-purchases.R b/tests/testthat/test-include-gld-purchases.R
new file mode 100644
index 0000000..354302b
--- /dev/null
+++ b/tests/testthat/test-include-gld-purchases.R
@@ -0,0 +1,102 @@
+constants <- tibble::tibble(
+  pnr = "2132131231",
+  eksd = "20210101",
+  volume = 1.1,
+  apk = 1.1,
+  indo = "324314324",
+  name = "random",
+  vnr = "123123"
+)
+
+lmdb <- tibble::tribble(
+  ~atc,
+  "A10abc",
+  "A10",
+  "A10123",
+  "A11",
+  "A21",
+  "B10A10",
+) |>
+  dplyr::bind_cols(constants)
+
+expected <- tibble::tribble(
+  ~atc,
+  "A10abc",
+  "A10",
+  "A10123",
+) |>
+  dplyr::bind_cols(constants) |>
+  dplyr::rename(date = eksd) |>
+  dplyr::relocate(atc, .after = date)
+
+test_that("dataset needs expected variables", {
+  actual <- lmdb[-2]
+  expect_error(include_gld_purchases(actual))
+})
+
+test_that("those with inclusion are kept", {
+  actual <- include_gld_purchases(lmdb)
+  expect_equal(actual, expected)
+})
+
+test_that("casing of input variables doesn't matter", {
+  actual <- lmdb |>
+    dplyr::rename_with(\(columns) toupper(columns)) |>
+    include_gld_purchases()
+  expect_equal(actual, expected)
+})
+
+test_that("verification works for DuckDB Database", {
+  skip_on_cran()
+  skip_if_not_installed("duckplyr")
+  actual <- duckplyr::as_duckplyr_tibble(lmdb) |>
+    include_gld_purchases()
+
+  actual_rows <- actual |>
+    dplyr::count() |>
+    dplyr::pull(n)
+
+  expect_equal(actual_rows, nrow(expected))
+  expect_equal(colnames(actual), colnames(expected))
+})
+
+test_that("verification works for Arrow Tables (from Parquet)", {
+  skip_on_cran()
+  skip_if_not_installed("arrow")
+  actual <- arrow::as_arrow_table(lmdb) |>
+    include_gld_purchases()
+
+  actual_rows <- actual |>
+    dplyr::count() |>
+    dplyr::pull(n)
+
+  expect_equal(actual_rows, nrow(expected))
+  # TODO: Arrow doesn't work with colname(), fix?
+  expect_equal(names(actual), colnames(expected))
+})
+
+test_that("verification works for data.frame", {
+  actual <- as.data.frame(lmdb) |>
+    include_gld_purchases()
+
+  actual_rows <- actual |>
+    dplyr::count() |>
+    dplyr::pull(n)
+
+  expect_equal(actual_rows, nrow(expected))
+  expect_equal(colnames(actual), colnames(expected))
+})
+
+test_that("verification works for data.table", {
+  skip_on_cran()
+  skip_if_not_installed("data.table")
+  actual <- data.table::as.data.table(lmdb) |>
+    include_gld_purchases()
+
+  actual_rows <- actual |>
+    dplyr::count() |>
+    dplyr::pull(n)
+
+  expect_equal(actual_rows, nrow(expected))
+  expect_equal(colnames(actual), colnames(expected))
+})