<entry id="2221913" stat="A" corpus="jmdict" type="jmdict">
<ent_corp type="jmdict">jmdict</ent_corp>
<ent_seq>2211060</ent_seq>
<k_ele>
<keb>薬が効く</keb>
</k_ele>
<k_ele>
<keb>薬がきく</keb>
<ke_inf>&sK;</ke_inf>
</k_ele>
<k_ele>
<keb>クスリが効く</keb>
<ke_inf>&sK;</ke_inf>
</k_ele>
<r_ele>
<reb>くすりがきく</reb>
</r_ele>
<sense>
<pos>&exp;</pos>
<pos>&v5k;</pos>
<gloss>to have medicine be effective</gloss>
</sense>
<info>
<audit time="2007-10-06 00:00:00" stat="A">
<upd_detl>Entry created</upd_detl>
</audit>
<audit time="2023-02-15 04:22:27" stat="A" unap="true">
<upd_name>Stephen Kraus</upd_name>
<upd_email>...address hidden...</upd_email>
<upd_refs>This is in sankoku as 「くすりがきく」.
I don't see a ref for 「やくがきく」. Sounds unlikely to me

Google N-gram Corpus Counts
╭─ーーーーーーー─┬────────┬───────╮
│ 薬が効いて　　 │ 50,268 │ 94.6% │
│ 薬がきいて　　 │  1,622 │  3.1% │ - adding
│ クスリが効いて │    979 │  1.8% │ - adding
│ くすりが効いて │    128 │  0.2% │
│ ヤクが効いて　 │     86 │  0.2% │
│ やくが効いて　 │      0 │  0.0% │
│ やくがきいて　 │      0 │  0.0% │
│ くすりがきいて │     42 │  0.1% │ - adding
╰─ーーーーーーー─┴────────┴───────╯</upd_refs>
<upd_diff>@@ -6,0 +7,11 @@
+&lt;k_ele&gt;
+&lt;keb&gt;薬がきく&lt;/keb&gt;
+&lt;ke_inf&gt;&amp;sK;&lt;/ke_inf&gt;
+&lt;/k_ele&gt;
+&lt;k_ele&gt;
+&lt;keb&gt;クスリが効く&lt;/keb&gt;
+&lt;ke_inf&gt;&amp;sK;&lt;/ke_inf&gt;
+&lt;/k_ele&gt;
+&lt;r_ele&gt;
+&lt;reb&gt;くすりがきく&lt;/reb&gt;
+&lt;/r_ele&gt;</upd_diff>
</audit>
<audit time="2023-02-15 06:01:09" stat="A">
<upd_uid>jwb</upd_uid>
<upd_name>Jim Breen</upd_name>
<upd_email>...address hidden...</upd_email>
<upd_detl>I think it can go.</upd_detl>
<upd_diff>@@ -17,3 +16,0 @@
-&lt;/r_ele&gt;
-&lt;r_ele&gt;
-&lt;reb&gt;やくがきく&lt;/reb&gt;</upd_diff>
</audit>
</info>
</entry>