diff --git a/redbot/cogs/filter/filter.py b/redbot/cogs/filter/filter.py
index 716bd5af1..b445f6e38 100644
--- a/redbot/cogs/filter/filter.py
+++ b/redbot/cogs/filter/filter.py
@@ -7,7 +7,6 @@ from redbot.core.bot import Red
 from redbot.core.i18n import Translator, cog_i18n
 from redbot.core.utils.chat_formatting import pagify
 
-RE_WORD_SPLIT = re.compile(r"[^\w]")
 _ = Translator("Filter", __file__)
 
 
@@ -32,6 +31,7 @@ class Filter(commands.Cog):
         self.settings.register_member(**default_member_settings)
         self.settings.register_channel(**default_channel_settings)
         self.register_task = self.bot.loop.create_task(self.register_filterban())
+        self.pattern_cache = {}
 
     def __unload(self):
         self.register_task.cancel()
@@ -165,6 +165,7 @@ class Filter(commands.Cog):
                     tmp += word + " "
         added = await self.add_to_filter(channel, word_list)
         if added:
+            self.invalidate_cache(ctx.guild, ctx.channel)
             await ctx.send(_("Words added to filter."))
         else:
             await ctx.send(_("Words already in the filter."))
@@ -198,6 +199,7 @@ class Filter(commands.Cog):
         removed = await self.remove_from_filter(channel, word_list)
         if removed:
             await ctx.send(_("Words removed from filter."))
+            self.invalidate_cache(ctx.guild, ctx.channel)
         else:
             await ctx.send(_("Those words weren't in the filter."))
 
@@ -229,6 +231,7 @@ class Filter(commands.Cog):
                     tmp += word + " "
         added = await self.add_to_filter(server, word_list)
         if added:
+            self.invalidate_cache(ctx.guild)
             await ctx.send(_("Words successfully added to filter."))
         else:
             await ctx.send(_("Those words were already in the filter."))
@@ -261,6 +264,7 @@ class Filter(commands.Cog):
                     tmp += word + " "
         removed = await self.remove_from_filter(server, word_list)
         if removed:
+            self.invalidate_cache(ctx.guild)
             await ctx.send(_("Words successfully removed from filter."))
         else:
             await ctx.send(_("Those words weren't in the filter."))
@@ -279,6 +283,10 @@ class Filter(commands.Cog):
         else:
             await ctx.send(_("Names and nicknames will now be filtered."))
 
+    def invalidate_cache(self, guild: discord.Guild, channel: discord.TextChannel = None):
+        """ Invalidate a cached pattern"""
+        self.pattern_cache.pop((guild, channel), None)
+
     async def add_to_filter(
         self, server_or_channel: Union[discord.Guild, discord.TextChannel], words: list
     ) -> bool:
@@ -322,24 +330,34 @@ class Filter(commands.Cog):
     async def filter_hits(
         self, text: str, server_or_channel: Union[discord.Guild, discord.TextChannel]
     ) -> Set[str]:
-        if isinstance(server_or_channel, discord.Guild):
-            word_list = set(await self.settings.guild(server_or_channel).filter())
-        elif isinstance(server_or_channel, discord.TextChannel):
-            word_list = set(
-                await self.settings.guild(server_or_channel.guild).filter()
-                + await self.settings.channel(server_or_channel).filter()
-            )
-        else:
-            raise TypeError("%r should be Guild or TextChannel" % server_or_channel)
 
-        content = text.lower()
-        msg_words = set(RE_WORD_SPLIT.split(content))
+        try:
+            guild = server_or_channel.guild
+            channel = server_or_channel
+        except AttributeError:
+            guild = server_or_channel
+            channel = None
 
-        filtered_phrases = {x for x in word_list if len(RE_WORD_SPLIT.split(x)) > 1}
-        filtered_words = word_list - filtered_phrases
+        hits: Set[str] = set()
 
-        hits = {p for p in filtered_phrases if p in content}
-        hits |= filtered_words & msg_words
+        try:
+            pattern = self.pattern_cache[(guild, channel)]
+        except KeyError:
+            word_list = set(await self.settings.guild(guild).filter())
+            if channel:
+                word_list |= set(await self.settings.channel(channel).filter())
+
+            if word_list:
+                pattern = re.compile(
+                    "|".join(rf"\b{re.escape(w)}\b" for w in word_list), flags=re.I
+                )
+            else:
+                pattern = None
+
+            self.pattern_cache[(guild, channel)] = pattern
+
+        if pattern:
+            hits |= set(pattern.findall(text))
         return hits
 
     async def check_filter(self, message: discord.Message):