How to add a menu tab to a user profile?
You should implement hook_menu_alter() instead of hook_menu.

function add_menu_tab_menu_alter(&amp;$items) {
  $items['user/dashboard']['type'] = MENU_LOCAL_TASK;
}


Then you should clear the cache, at least the menu cache, as Mołot suggested.

There is also another approach using hook_menu_local_tasks_alter(). But the first method is better since it is called only once, after the hook_menu and saved in the database, while the latter is being called each time the local tasks are rendered.