diff --git a/src/components/Dashboard.tsx b/src/components/Dashboard.tsx
index f860823..1177733 100644
--- a/src/components/Dashboard.tsx
+++ b/src/components/Dashboard.tsx
@@ -1,6 +1,6 @@
 'use client';
 
-import { useState, useEffect } from 'react';
+import { useState, useEffect, useCallback } from 'react';
 import { User } from '@/lib/session';
 import {
   getUsageData,
@@ -34,14 +34,17 @@ export function Dashboard({ user }: DashboardProps) {
   const [showSetup, setShowSetup] = useState(false);
   const [showUsagePrompt, setShowUsagePrompt] = useState(false);
   const [isLoading, setIsLoading] = useState(true);
+  const [refreshKey, setRefreshKey] = useState(0);
 
-  const loadData = () => {
-    const prefs = getPreferences();
-    const usage = getUsageData();
+  const loadData = useCallback(() => {
+    // Always pass user.id explicitly to ensure correct data is loaded
+    const prefs = getPreferences(user.id);
+    const usage = getUsageData(user.id);
     setPreferences(prefs);
     setUsageData(usage);
+    setRefreshKey(prev => prev + 1);
     return prefs;
-  };
+  }, [user.id]);
 
   useEffect(() => {
     // Set the current user ID for all storage operations
@@ -56,7 +59,7 @@ export function Dashboard({ user }: DashboardProps) {
     }
 
     setIsLoading(false);
-  }, [user.id]);
+  }, [user.id, loadData]);
 
   const handleSetupComplete = (data: { substance: 'nicotine' | 'weed'; name: string; age: number }) => {
     const today = new Date().toISOString().split('T')[0];
@@ -69,35 +72,41 @@ export function Dashboard({ user }: DashboardProps) {
       userName: data.name,
       userAge: data.age,
     };
-    savePreferences(newPrefs);
+    savePreferences(newPrefs, user.id);
     setPreferences(newPrefs);
     setShowSetup(false);
     setShowUsagePrompt(true);
+    setRefreshKey(prev => prev + 1);
   };
 
   const handleUsageSubmit = (count: number) => {
-    if (!preferences || count === 0) {
+    if (!preferences) {
       setShowUsagePrompt(false);
-      loadData();
       return;
     }
 
-    const today = new Date().toISOString().split('T')[0];
-    saveUsageEntry({
-      date: today,
-      count,
-      substance: preferences.substance,
-    });
+    if (count > 0) {
+      const today = new Date().toISOString().split('T')[0];
+      saveUsageEntry({
+        date: today,
+        count,
+        substance: preferences.substance,
+      }, user.id);
+    }
+
     setShowUsagePrompt(false);
-    loadData();
+    // Reload data and force calendar refresh
+    const usage = getUsageData(user.id);
+    setUsageData(usage);
+    setRefreshKey(prev => prev + 1);
   };
 
   const handleGeneratePlan = () => {
     if (!preferences) return;
 
-    const plan = generateQuitPlan(preferences.substance);
+    const plan = generateQuitPlan(preferences.substance, user.id);
     const updatedPrefs = { ...preferences, quitPlan: plan };
-    savePreferences(updatedPrefs);
+    savePreferences(updatedPrefs, user.id);
     setPreferences(updatedPrefs);
   };
 
@@ -138,9 +147,11 @@ export function Dashboard({ user }: DashboardProps) {
             <div className="grid gap-6 md:grid-cols-2">
               <div className="space-y-6">
                 <UsageCalendar
+                  key={refreshKey}
                   usageData={usageData}
                   substance={preferences.substance}
                   onDataUpdate={loadData}
+                  userId={user.id}
                 />
               </div>
               <div className="space-y-6">
@@ -148,9 +159,9 @@ export function Dashboard({ user }: DashboardProps) {
                 <QuitPlanCard
                   plan={preferences.quitPlan}
                   onGeneratePlan={handleGeneratePlan}
-                  hasEnoughData={hasOneWeekOfData(preferences.substance)}
+                  hasEnoughData={hasOneWeekOfData(preferences.substance, user.id)}
                   daysTracked={getDaysTracked()}
-                  currentAverage={calculateWeeklyAverage(preferences.substance)}
+                  currentAverage={calculateWeeklyAverage(preferences.substance, user.id)}
                 />
               </div>
             </div>
@@ -166,6 +177,7 @@ export function Dashboard({ user }: DashboardProps) {
           onClose={() => setShowUsagePrompt(false)}
           onSubmit={handleUsageSubmit}
           substance={preferences.substance}
+          userId={user.id}
         />
       )}
     </div>
diff --git a/src/components/UsageCalendar.tsx b/src/components/UsageCalendar.tsx
index c6f862f..dfc4427 100644
--- a/src/components/UsageCalendar.tsx
+++ b/src/components/UsageCalendar.tsx
@@ -19,9 +19,10 @@ interface UsageCalendarProps {
   usageData: UsageEntry[];
   substance: 'nicotine' | 'weed';
   onDataUpdate: () => void;
+  userId: string;
 }
 
-export function UsageCalendar({ usageData, substance, onDataUpdate }: UsageCalendarProps) {
+export function UsageCalendar({ usageData, substance, onDataUpdate, userId }: UsageCalendarProps) {
   const [selectedDate, setSelectedDate] = useState<Date | undefined>(undefined);
   const [editCount, setEditCount] = useState('');
   const [isEditing, setIsEditing] = useState(false);
@@ -36,7 +37,7 @@ export function UsageCalendar({ usageData, substance, onDataUpdate }: UsageCalen
 
     setSelectedDate(date);
     const dateStr = date.toISOString().split('T')[0];
-    const currentCount = getUsageForDate(dateStr, substance);
+    const currentCount = getUsageForDate(dateStr, substance, userId);
     setEditCount(currentCount.toString());
     setIsEditing(true);
   };
@@ -45,7 +46,7 @@ export function UsageCalendar({ usageData, substance, onDataUpdate }: UsageCalen
     if (selectedDate) {
       const dateStr = selectedDate.toISOString().split('T')[0];
       const newCount = parseInt(editCount, 10) || 0;
-      setUsageForDate(dateStr, newCount, substance);
+      setUsageForDate(dateStr, newCount, substance, userId);
       onDataUpdate();
     }
     setIsEditing(false);
@@ -62,7 +63,7 @@ export function UsageCalendar({ usageData, substance, onDataUpdate }: UsageCalen
   const handleClearDay = () => {
     if (selectedDate) {
       const dateStr = selectedDate.toISOString().split('T')[0];
-      clearDayData(dateStr, substance);
+      clearDayData(dateStr, substance, userId);
       onDataUpdate();
     }
     setIsEditing(false);
diff --git a/src/components/UsagePromptDialog.tsx b/src/components/UsagePromptDialog.tsx
index 4e913b8..7208dc2 100644
--- a/src/components/UsagePromptDialog.tsx
+++ b/src/components/UsagePromptDialog.tsx
@@ -18,6 +18,7 @@ interface UsagePromptDialogProps {
   onClose: () => void;
   onSubmit: (count: number) => void;
   substance: 'nicotine' | 'weed';
+  userId: string;
 }
 
 export function UsagePromptDialog({
@@ -25,6 +26,7 @@ export function UsagePromptDialog({
   onClose,
   onSubmit,
   substance,
+  userId,
 }: UsagePromptDialogProps) {
   const [wantsToLog, setWantsToLog] = useState<boolean | null>(null);
   const [count, setCount] = useState('1');
@@ -33,7 +35,7 @@ export function UsagePromptDialog({
   const substanceLabelPlural = substance === 'nicotine' ? 'puffs/cigarettes' : 'hits';
 
   const today = new Date().toISOString().split('T')[0];
-  const todayCount = typeof window !== 'undefined' ? getUsageForDate(today, substance) : 0;
+  const todayCount = typeof window !== 'undefined' ? getUsageForDate(today, substance, userId) : 0;
 
   const handleSubmit = () => {
     if (wantsToLog === true && count) {
diff --git a/src/components/UserHeader.tsx b/src/components/UserHeader.tsx
index b898a71..326ffb3 100644
--- a/src/components/UserHeader.tsx
+++ b/src/components/UserHeader.tsx
@@ -14,9 +14,9 @@ export function UserHeader({ user }: UserHeaderProps) {
   const [userName, setUserName] = useState<string | null>(null);
 
   useEffect(() => {
-    const prefs = getPreferences();
+    const prefs = getPreferences(user.id);
     setUserName(prefs.userName);
-  }, []);
+  }, [user.id]);
 
   const initials = [user.firstName?.[0], user.lastName?.[0]]
     .filter(Boolean)