diff --git a/src/components/settings.tsx b/src/components/settings.tsx
index 07b567d..8348c8c 100644
--- a/src/components/settings.tsx
+++ b/src/components/settings.tsx
@@ -394,11 +394,12 @@ const Settings = ({
                       min={0}
                       max={500}
                       placeholder={t('min')}
-                      required={true}
-                      error={!!therapeuticRangeError || !therapeuticRange.min}
-                      errorMessage={formatText(therapeuticRangeError || t('errorTherapeuticRangeMinRequired') || 'Minimum therapeutic range is required')}
+                      required={false}
+                      error={!!therapeuticRangeError}
+                      errorMessage={formatText(therapeuticRangeError)}
                       showResetButton={true}
                       defaultValue={defaultsForT.therapeuticRangeMin}
+                      allowEmpty={true}
                     />
                     <span className="text-muted-foreground">-</span>
                     <FormNumericInput
@@ -409,11 +410,12 @@ const Settings = ({
                       max={500}
                       placeholder={t('max')}
                       unit="ng/ml"
-                      required={true}
-                      error={!!therapeuticRangeError || !therapeuticRange.max}
-                      errorMessage={formatText(therapeuticRangeError || t('errorTherapeuticRangeMaxRequired') || 'Maximum therapeutic range is required')}
+                      required={false}
+                      error={!!therapeuticRangeError}
+                      errorMessage={formatText(therapeuticRangeError)}
                       showResetButton={true}
                       defaultValue={defaultsForT.therapeuticRangeMax}
+                      allowEmpty={true}
                     />
                   </div>
                 </div>
diff --git a/src/components/simulation-chart.tsx b/src/components/simulation-chart.tsx
index d6983c7..94eee0a 100644
--- a/src/components/simulation-chart.tsx
+++ b/src/components/simulation-chart.tsx
@@ -638,20 +638,20 @@ const SimulationChart = React.memo(({
                 />
               );
             })}
-            {showTherapeuticRange && (chartView === 'damph' || chartView === 'both') && (
+            {showTherapeuticRange && (chartView === 'damph' || chartView === 'both') && therapeuticRange.min && !isNaN(parseFloat(therapeuticRange.min)) && (
               <ReferenceLine
-                y={parseFloat(therapeuticRange.min) || 0}
-                label={{ value: t('refLineMin'), position: 'insideTopLeft' }}
+                y={parseFloat(therapeuticRange.min)}
+                label={{ value: t('refLineMin'), position: 'insideBottomLeft', style: { fontSize: '0.75rem', fontStyle: 'italic', fill: CHART_COLORS.therapeuticMin } }}
                 stroke={CHART_COLORS.therapeuticMin}
                 strokeDasharray="3 3"
                 xAxisId="hours"
                 yAxisId="concentration"
               />
             )}
-            {showTherapeuticRange && (chartView === 'damph' || chartView === 'both') && (
+            {showTherapeuticRange && (chartView === 'damph' || chartView === 'both') && therapeuticRange.max && !isNaN(parseFloat(therapeuticRange.max)) && (
               <ReferenceLine
-                y={parseFloat(therapeuticRange.max) || 0}
-                label={{ value: t('refLineMax'), position: 'insideTopLeft' }}
+                y={parseFloat(therapeuticRange.max)}
+                label={{ value: t('refLineMax'), position: 'insideTopLeft', style: { fontSize: '0.75rem', fontStyle: 'italic', fill: CHART_COLORS.therapeuticMax } }}
                 stroke={CHART_COLORS.therapeuticMax}
                 strokeDasharray="3 3"
                 xAxisId="hours"