diff --git a/frontend_tests/node_tests/dispatch.js b/frontend_tests/node_tests/dispatch.js
index fcda618171..dbe687a146 100644
--- a/frontend_tests/node_tests/dispatch.js
+++ b/frontend_tests/node_tests/dispatch.js
@@ -190,6 +190,7 @@ const event_fixtures = {
         op: 'add',
         message_id: 128,
         emoji_name: 'anguished_pig',
+        user_id: "1",
         user: {
             id: "1",
         },
@@ -200,6 +201,7 @@ const event_fixtures = {
         op: 'remove',
         message_id: 256,
         emoji_name: 'angery',
+        user_id: "1",
         user: {
             id: "1",
         },
diff --git a/frontend_tests/node_tests/reactions.js b/frontend_tests/node_tests/reactions.js
index 6b2efdf4a0..bc6255457e 100644
--- a/frontend_tests/node_tests/reactions.js
+++ b/frontend_tests/node_tests/reactions.js
@@ -74,15 +74,15 @@ people.add(cali);
 const message = {
     id: 1001,
     reactions: [
-        {emoji_name: 'smile', user: {id: 5}, reaction_type: 'unicode_emoji', emoji_code: '263a'},
-        {emoji_name: 'smile', user: {id: 6}, reaction_type: 'unicode_emoji', emoji_code: '263a'},
-        {emoji_name: 'frown', user: {id: 7}, reaction_type: 'unicode_emoji', emoji_code: '1f641'},
-        {emoji_name: 'inactive_realm_emoji', user: {id: 5}, reaction_type: 'realm_emoji',
+        {emoji_name: 'smile', user_id: 5, reaction_type: 'unicode_emoji', emoji_code: '263a'},
+        {emoji_name: 'smile', user_id: 6, reaction_type: 'unicode_emoji', emoji_code: '263a'},
+        {emoji_name: 'frown', user_id: 7, reaction_type: 'unicode_emoji', emoji_code: '1f641'},
+        {emoji_name: 'inactive_realm_emoji', user_id: 5, reaction_type: 'realm_emoji',
          emoji_code: '992'},
 
         // add some bogus user_ids
-        {emoji_name: 'octopus', user: {id: 8888}, reaction_type: 'unicode_emoji', emoji_code: '1f419'},
-        {emoji_name: 'frown', user: {id: 9999}, reaction_type: 'unicode_emoji', emoji_code: '1f641'},
+        {emoji_name: 'octopus', user_id: 8888, reaction_type: 'unicode_emoji', emoji_code: '1f419'},
+        {emoji_name: 'frown', user_id: 9999, reaction_type: 'unicode_emoji', emoji_code: '1f641'},
     ],
 };
 
@@ -298,9 +298,7 @@ run_test('add_and_remove_reaction', () => {
         reaction_type: 'unicode_emoji',
         emoji_name: '8ball',
         emoji_code: '1f3b1',
-        user: {
-            user_id: alice.user_id,
-        },
+        user_id: alice.user_id,
     };
 
     const message_reactions = $.create('our-reactions');
@@ -355,9 +353,7 @@ run_test('add_and_remove_reaction', () => {
         reaction_type: 'unicode_emoji',
         emoji_name: '8ball',
         emoji_code: '1f3b1',
-        user: {
-            user_id: bob.user_id,
-        },
+        user_id: bob.user_id,
     };
 
     const count_element = $.create('count-element');
@@ -402,9 +398,7 @@ run_test('add_and_remove_reaction', () => {
         reaction_type: 'realm_emoji',
         emoji_name: 'realm_emoji',
         emoji_code: '991',
-        user: {
-            user_id: cali.user_id,
-        },
+        user_id: cali.user_id,
     };
 
     template_called = false;
@@ -430,9 +424,7 @@ run_test('add_and_remove_reaction', () => {
         reaction_type: 'realm_emoji',
         emoji_name: 'realm_emoji',
         emoji_code: '991',
-        user: {
-            user_id: alice.user_id,
-        },
+        user_id: alice.user_id,
     };
 
     message_reactions.find = function (selector) {
@@ -495,9 +487,7 @@ run_test('with_view_stubs', () => {
         reaction_type: 'unicode_emoji',
         emoji_name: '8ball',
         emoji_code: '1f3b1',
-        user: {
-            user_id: alice.user_id,
-        },
+        user_id: alice.user_id,
     };
 
     const bob_8ball_event = {
@@ -505,9 +495,7 @@ run_test('with_view_stubs', () => {
         reaction_type: 'unicode_emoji',
         emoji_name: '8ball',
         emoji_code: '1f3b1',
-        user: {
-            user_id: bob.user_id,
-        },
+        user_id: bob.user_id,
     };
 
     const cali_airplane_event = {
@@ -515,9 +503,7 @@ run_test('with_view_stubs', () => {
         reaction_type: 'unicode_emoji',
         emoji_name: 'airplane',
         emoji_code: '2708',
-        user: {
-            user_id: cali.user_id,
-        },
+        user_id: cali.user_id,
     };
 
     test_view_calls({
@@ -627,9 +613,7 @@ run_test('error_handling', () => {
         reaction_type: 'realm_emoji',
         emoji_name: 'realm_emoji',
         emoji_code: '991',
-        user: {
-            user_id: 99,
-        },
+        user_id: 99,
     };
 
     const original_func = reactions.current_user_has_reacted_to_emoji;
@@ -653,9 +637,7 @@ run_test('remove spurious user', () => {
         emoji_name: 'frown',
         emoji_code: '1f641',
         message_id: message.id,
-        user: {
-            user_id: alice.user_id,
-        },
+        user_id: alice.user_id,
     };
 
     reactions.remove_reaction(event);
@@ -676,9 +658,7 @@ run_test('remove last user', () => {
         emoji_name: 'frown',
         emoji_code: '1f641',
         message_id: message.id,
-        user: {
-            user_id: cali.user_id,
-        },
+        user_id: cali.user_id,
     };
     reactions.remove_reaction(event);
 
@@ -745,8 +725,7 @@ run_test('code coverage', () => {
     };
 
     reactions.remove_reaction({
-        message_id: 42,
-        user: {},
+        message_id: 42, // TODO: REACTIONS API
     });
 });
 
@@ -754,8 +733,8 @@ run_test('duplicates', () => {
     const dup_reaction_message = {
         id: 1001,
         reactions: [
-            {emoji_name: 'smile', user: {id: 5}, reaction_type: 'unicode_emoji', emoji_code: '263a'},
-            {emoji_name: 'smile', user: {id: 5}, reaction_type: 'unicode_emoji', emoji_code: '263a'},
+            {emoji_name: 'smile', user_id: 5, reaction_type: 'unicode_emoji', emoji_code: '263a'},
+            {emoji_name: 'smile', user_id: 5, reaction_type: 'unicode_emoji', emoji_code: '263a'},
         ],
     };
 
diff --git a/static/js/reactions.js b/static/js/reactions.js
index 355740ce47..a576a5de2d 100644
--- a/static/js/reactions.js
+++ b/static/js/reactions.js
@@ -41,10 +41,7 @@ function get_message(message_id) {
 function create_reaction(message_id, reaction_info) {
     return {
         message_id: message_id,
-        user: {
-            user_id: page_params.user_id,
-            id: page_params.user_id,
-        },
+        user_id: page_params.user_id,
         local_id: exports.get_local_reaction_id(reaction_info),
         reaction_type: reaction_info.reaction_type,
         emoji_name: reaction_info.emoji_name,
@@ -218,7 +215,7 @@ exports.add_reaction = function (event) {
     exports.set_clean_reactions(message);
 
     const local_id = exports.get_local_reaction_id(event);
-    const user_id = event.user.user_id;
+    const user_id = event.user_id;
 
     const r = message.clean_reactions.get(local_id);
 
@@ -326,7 +323,7 @@ exports.remove_reaction = function (event) {
     const emoji_name = event.emoji_name;
     const emoji_code = event.emoji_code;
     const message_id = event.message_id;
-    const user_id = event.user.user_id;
+    const user_id = event.user_id;
     const message = message_store.get(message_id);
     const local_id = exports.get_local_reaction_id(event);
 
@@ -441,7 +438,7 @@ exports.set_clean_reactions = function (message) {
 
     for (const reaction of message.reactions) {
         const local_id = exports.get_local_reaction_id(reaction);
-        const user_id = reaction.user.id;
+        const user_id = reaction.user_id;
 
         if (!people.is_known_user_id(user_id)) {
             blueslip.warn('Unknown user_id ' + user_id +
diff --git a/templates/zerver/api/get-messages.md b/templates/zerver/api/get-messages.md
index dd4ce2f55c..0184a2e10e 100644
--- a/templates/zerver/api/get-messages.md
+++ b/templates/zerver/api/get-messages.md
@@ -103,6 +103,20 @@ present in all Zulip API responses).
       displayed sorted by ID.
     * `is_me_message`: Whether the message is a [/me status message][status-messages]
     * `reactions`: Data on any reactions to the message.
+        * `emoji_code`: An encoded version of the emoji's unicode codepoint.
+        * `emoji_name`: Name of the emoji.
+        * `reaction_type`: If the reaction uses a [custom emoji](/help/add-custom-emoji),
+          `reaction_type` will be set to `realm_emoji`.
+        * `user_id`: The ID of the user who added the reaction.
+           **Changes**: New in Zulip 2.2. The `user` object is
+           deprecated and will be removed in the future.
+        * `user`: Dictionary with data on the user who added the reaction, including
+           the user ID as the `id` field.  **Note**: In the [events
+           API](/api/get-events-from-queue), this `user` dictionary
+           confusing had the user ID in a field called `user_id`
+           instead.  We recommend ignoring fields other than the user
+           ID.  **Deprecated** and to be removed in a future release
+           once core clients have migrated to use the `user_id` field.
     * `recipient_id`: A unique ID for the set of users receiving the
       message (either a stream or group of users).  Useful primarily
       for hashing.
diff --git a/zerver/lib/actions.py b/zerver/lib/actions.py
index 9932c62c66..210fbabdda 100644
--- a/zerver/lib/actions.py
+++ b/zerver/lib/actions.py
@@ -1670,6 +1670,10 @@ def notify_reaction_update(user_profile: UserProfile, message: Message,
     event: Dict[str, Any] = {
         'type': 'reaction',
         'op': op,
+        'user_id': user_profile.id,
+        # TODO: We plan to remove this redundant user_dict object once
+        # clients are updated to support accessing use user_id.  See
+        # https://github.com/zulip/zulip/pull/14711 for details.
         'user': user_dict,
         'message_id': message.id,
         'emoji_name': reaction.emoji_name,
diff --git a/zerver/lib/message.py b/zerver/lib/message.py
index 2d259c4ad9..eb237bdf75 100644
--- a/zerver/lib/message.py
+++ b/zerver/lib/message.py
@@ -556,9 +556,17 @@ class ReactionDict:
         return {'emoji_name': row['emoji_name'],
                 'emoji_code': row['emoji_code'],
                 'reaction_type': row['reaction_type'],
+                # TODO: We plan to remove this redundant user dictionary once
+                # clients are updated to support accessing use user_id.  See
+                # https://github.com/zulip/zulip/pull/14711 for details.
+                #
+                # When we do that, we can likely update the `.values()` query to
+                # not fetch the extra user_profile__* fields from the database
+                # as a small performance optimization.
                 'user': {'email': row['user_profile__email'],
                          'id': row['user_profile__id'],
-                         'full_name': row['user_profile__full_name']}}
+                         'full_name': row['user_profile__full_name']},
+                'user_id': row['user_profile__id']}
 
 
 def access_message(user_profile: UserProfile, message_id: int) -> Tuple[Message, Optional[UserMessage]]:
diff --git a/zerver/tests/test_events.py b/zerver/tests/test_events.py
index e43420f6b1..cd6d1372d5 100644
--- a/zerver/tests/test_events.py
+++ b/zerver/tests/test_events.py
@@ -846,6 +846,7 @@ class EventsRegisterTest(ZulipTestCase):
             ('emoji_name', check_string),
             ('emoji_code', check_string),
             ('reaction_type', check_string),
+            ('user_id', check_int),
             ('user', check_dict_only([
                 ('email', check_string),
                 ('full_name', check_string),
@@ -871,6 +872,7 @@ class EventsRegisterTest(ZulipTestCase):
             ('emoji_name', check_string),
             ('emoji_code', check_string),
             ('reaction_type', check_string),
+            ('user_id', check_int),
             ('user', check_dict_only([
                 ('email', check_string),
                 ('full_name', check_string),
@@ -897,6 +899,7 @@ class EventsRegisterTest(ZulipTestCase):
             ('emoji_name', check_string),
             ('emoji_code', check_string),
             ('reaction_type', check_string),
+            ('user_id', check_int),
             ('user', check_dict_only([
                 ('email', check_string),
                 ('full_name', check_string),
@@ -951,6 +954,7 @@ class EventsRegisterTest(ZulipTestCase):
             ('emoji_name', check_string),
             ('emoji_code', check_string),
             ('reaction_type', check_string),
+            ('user_id', check_int),
             ('user', check_dict_only([
                 ('email', check_string),
                 ('full_name', check_string),
diff --git a/zerver/tests/test_messages.py b/zerver/tests/test_messages.py
index 82466ab656..e42b5423a2 100644
--- a/zerver/tests/test_messages.py
+++ b/zerver/tests/test_messages.py
@@ -1527,6 +1527,7 @@ class MessageDictTest(ZulipTestCase):
         msg_dict = MessageDict.build_dict_from_raw_db_row(row)
         self.assertEqual(msg_dict['reactions'][0]['emoji_name'],
                          reaction.emoji_name)
+        self.assertEqual(msg_dict['reactions'][0]['user_id'], sender.id)
         self.assertEqual(msg_dict['reactions'][0]['user']['id'],
                          sender.id)
         self.assertEqual(msg_dict['reactions'][0]['user']['email'],