diff --git a/app/assets/javascripts/sidebar/services/sidebar_service.js b/app/assets/javascripts/sidebar/services/sidebar_service.js
index ace2a163adc365890c84bde85eec81b12217a7db..cea26acd101dc6809855d1d2a52ca195c1795933 100644
--- a/app/assets/javascripts/sidebar/services/sidebar_service.js
+++ b/app/assets/javascripts/sidebar/services/sidebar_service.js
@@ -22,7 +22,6 @@ export default class SidebarService {
   constructor(endpointMap) {
     if (!SidebarService.singleton) {
       this.endpoint = endpointMap.endpoint;
-      this.toggleSubscriptionEndpoint = endpointMap.toggleSubscriptionEndpoint;
       this.moveIssueEndpoint = endpointMap.moveIssueEndpoint;
       this.projectsAutocompleteEndpoint = endpointMap.projectsAutocompleteEndpoint;
       this.fullPath = endpointMap.fullPath;
@@ -75,10 +74,6 @@ export default class SidebarService {
     });
   }
 
-  toggleSubscription() {
-    return axios.post(this.toggleSubscriptionEndpoint);
-  }
-
   moveIssue(moveToProjectId) {
     return axios.post(this.moveIssueEndpoint, {
       move_to_project_id: moveToProjectId,
diff --git a/app/assets/javascripts/sidebar/sidebar_mediator.js b/app/assets/javascripts/sidebar/sidebar_mediator.js
index 0a5e44a9b957259f3bfd0bce95a676b18def9c23..9144e3b08dbab1507d0b26f9322fb0e86f35b71c 100644
--- a/app/assets/javascripts/sidebar/sidebar_mediator.js
+++ b/app/assets/javascripts/sidebar/sidebar_mediator.js
@@ -17,7 +17,6 @@ export default class SidebarMediator {
     this.store = new Store(options);
     this.service = new Service({
       endpoint: options.endpoint,
-      toggleSubscriptionEndpoint: options.toggleSubscriptionEndpoint,
       moveIssueEndpoint: options.moveIssueEndpoint,
       projectsAutocompleteEndpoint: options.projectsAutocompleteEndpoint,
       fullPath: options.fullPath,
@@ -85,22 +84,6 @@ export default class SidebarMediator {
     this.store.setAssigneeData(data);
     this.store.setReviewerData(data);
     this.store.setTimeTrackingData(data);
-    this.store.setParticipantsData(data);
-    this.store.setSubscriptionsData(data);
-  }
-
-  toggleSubscription() {
-    this.store.setFetchingState('subscriptions', true);
-    return this.service
-      .toggleSubscription()
-      .then(() => {
-        this.store.setSubscribedState(!this.store.subscribed);
-        this.store.setFetchingState('subscriptions', false);
-      })
-      .catch((err) => {
-        this.store.setFetchingState('subscriptions', false);
-        throw err;
-      });
   }
 
   fetchAutocompleteProjects(searchTerm) {
diff --git a/app/assets/javascripts/sidebar/stores/sidebar_store.js b/app/assets/javascripts/sidebar/stores/sidebar_store.js
index 3c108b06eabb5c6a005fff79b43d1ed37b5d9b70..94c54fc098028cb886834546abc6d116c36a5aba 100644
--- a/app/assets/javascripts/sidebar/stores/sidebar_store.js
+++ b/app/assets/javascripts/sidebar/stores/sidebar_store.js
@@ -22,8 +22,6 @@ export default class SidebarStore {
     this.isFetching = {
       assignees: true,
       reviewers: true,
-      participants: true,
-      subscriptions: true,
     };
     this.isLoading = {};
     this.autocompleteProjects = [];
@@ -63,18 +61,6 @@ export default class SidebarStore {
     this.humanTotalTimeSpent = data.human_total_time_spent;
   }
 
-  setParticipantsData(data) {
-    this.isFetching.participants = false;
-    this.participants = data.participants || [];
-  }
-
-  setSubscriptionsData(data) {
-    this.projectEmailsDisabled = data.project_emails_disabled || false;
-    this.subscribeDisabledDescription = data.subscribe_disabled_description;
-    this.isFetching.subscriptions = false;
-    this.subscribed = data.subscribed || false;
-  }
-
   setFetchingState(key, value) {
     this.isFetching[key] = value;
   }
diff --git a/app/serializers/issuable_sidebar_extras_entity.rb b/app/serializers/issuable_sidebar_extras_entity.rb
index 77f2e34fa5d3b728f8dfcb7af2a111762e52b0e1..68c71cd5cf3f2a5af48d8e623db3806a3bb18678 100644
--- a/app/serializers/issuable_sidebar_extras_entity.rb
+++ b/app/serializers/issuable_sidebar_extras_entity.rb
@@ -3,23 +3,6 @@
 class IssuableSidebarExtrasEntity < Grape::Entity
   include RequestAwareEntity
   include TimeTrackableEntity
-  include NotificationsHelper
-
-  expose :participants, using: ::API::Entities::UserBasic do |issuable|
-    issuable.participants(request.current_user)
-  end
-
-  expose :project_emails_disabled do |issuable|
-    issuable.project.emails_disabled?
-  end
-
-  expose :subscribe_disabled_description do |issuable|
-    notification_description(:owner_disabled)
-  end
-
-  expose :subscribed do |issuable|
-    issuable.subscribed?(request.current_user, issuable.project)
-  end
 
   expose :assignees, using: ::API::Entities::UserBasic
 end
diff --git a/spec/frontend/sidebar/sidebar_mediator_spec.js b/spec/frontend/sidebar/sidebar_mediator_spec.js
index 019ded870930e684dd66f02844d6b797cec589ab..cb84c142d558dc485116bfa9e3fbd590f0f0a7b0 100644
--- a/spec/frontend/sidebar/sidebar_mediator_spec.js
+++ b/spec/frontend/sidebar/sidebar_mediator_spec.js
@@ -63,8 +63,6 @@ describe('Sidebar mediator', () => {
     expect(mediator.store.assignees).toEqual(mockData.assignees);
     expect(mediator.store.humanTimeEstimate).toEqual(mockData.human_time_estimate);
     expect(mediator.store.humanTotalTimeSpent).toEqual(mockData.human_total_time_spent);
-    expect(mediator.store.participants).toEqual(mockData.participants);
-    expect(mediator.store.subscribed).toEqual(mockData.subscribed);
     expect(mediator.store.timeEstimate).toEqual(mockData.time_estimate);
     expect(mediator.store.totalTimeSpent).toEqual(mockData.total_time_spent);
   });
@@ -117,19 +115,4 @@ describe('Sidebar mediator', () => {
       urlSpy.mockRestore();
     });
   });
-
-  it('toggle subscription', () => {
-    mediator.store.setSubscribedState(false);
-    mock.onPost(mediatorMockData.toggleSubscriptionEndpoint).reply(200, {});
-    const spy = jest
-      .spyOn(mediator.service, 'toggleSubscription')
-      .mockReturnValue(Promise.resolve());
-
-    return mediator.toggleSubscription().then(() => {
-      expect(spy).toHaveBeenCalled();
-      expect(mediator.store.subscribed).toEqual(true);
-
-      spy.mockRestore();
-    });
-  });
 });
diff --git a/spec/frontend/sidebar/sidebar_store_spec.js b/spec/frontend/sidebar/sidebar_store_spec.js
index 7b73dc868b72f1002a186c552e60a1408e3ea18f..3930dabfcfa39c8ae0150ded6f534c0edf1e6d06 100644
--- a/spec/frontend/sidebar/sidebar_store_spec.js
+++ b/spec/frontend/sidebar/sidebar_store_spec.js
@@ -16,17 +16,6 @@ const ANOTHER_ASSINEE = {
   avatar_url: 'https://www.gravatar.com/avatar/e64c7d89f26bd1972efa854d13d7dd61?s=80&d=identicon',
 };
 
-const PARTICIPANT = {
-  id: 1,
-  state: 'active',
-  username: 'marcene',
-  name: 'Allie Will',
-  web_url: 'foo.com',
-  avatar_url: 'gravatar.com/avatar/xxx',
-};
-
-const PARTICIPANT_LIST = [PARTICIPANT, { ...PARTICIPANT, id: 2 }, { ...PARTICIPANT, id: 3 }];
-
 describe('Sidebar store', () => {
   let testContext;
 
@@ -113,28 +102,6 @@ describe('Sidebar store', () => {
     expect(testContext.store.changing).toBe(true);
   });
 
-  it('sets participants data', () => {
-    expect(testContext.store.participants.length).toEqual(0);
-
-    testContext.store.setParticipantsData({
-      participants: PARTICIPANT_LIST,
-    });
-
-    expect(testContext.store.isFetching.participants).toEqual(false);
-    expect(testContext.store.participants.length).toEqual(PARTICIPANT_LIST.length);
-  });
-
-  it('sets subcriptions data', () => {
-    expect(testContext.store.subscribed).toEqual(null);
-
-    testContext.store.setSubscriptionsData({
-      subscribed: true,
-    });
-
-    expect(testContext.store.isFetching.subscriptions).toEqual(false);
-    expect(testContext.store.subscribed).toEqual(true);
-  });
-
   it('set assigned data', () => {
     const users = {
       assignees: UsersMockHelper.createNumberRandomUsers(3),
@@ -147,11 +114,11 @@ describe('Sidebar store', () => {
   });
 
   it('sets fetching state', () => {
-    expect(testContext.store.isFetching.participants).toEqual(true);
+    expect(testContext.store.isFetching.assignees).toEqual(true);
 
-    testContext.store.setFetchingState('participants', false);
+    testContext.store.setFetchingState('assignees', false);
 
-    expect(testContext.store.isFetching.participants).toEqual(false);
+    expect(testContext.store.isFetching.assignees).toEqual(false);
   });
 
   it('sets loading state', () => {
diff --git a/spec/serializers/issuable_sidebar_extras_entity_spec.rb b/spec/serializers/issuable_sidebar_extras_entity_spec.rb
index f49b9acfd5d1009d7394b9bf694115dd13a2145d..80c135cdc2261bbe21261ca40d812a177375420a 100644
--- a/spec/serializers/issuable_sidebar_extras_entity_spec.rb
+++ b/spec/serializers/issuable_sidebar_extras_entity_spec.rb
@@ -10,11 +10,7 @@
 
   subject { described_class.new(resource, request: request).as_json }
 
-  it 'have subscribe attributes' do
-    expect(subject).to include(:participants,
-                               :project_emails_disabled,
-                               :subscribe_disabled_description,
-                               :subscribed,
-                               :assignees)
+  it 'have assignee attribute' do
+    expect(subject).to include(:assignees)
   end
 end