Multiselect dropdown no Excel

gistfile1.vb

Private Sub Worksheet_Change(ByVal Target As Range)

Dim rngDV As Range
Dim oldVal As String
Dim newVal As String
If Target.Count > 1 Then GoTo exitHandler

On Error Resume Next
Set rngDV = Cells.SpecialCells(xlCellTypeAllValidation)
On Error GoTo exitHandler

If rngDV Is Nothing Then GoTo exitHandler

If Intersect(Target, rngDV) Is Nothing Then

Else
  Application.EnableEvents = False
  newVal = Target.Value
  Application.Undo
  oldVal = Target.Value
  Target.Value = newVal
  If oldVal = "" Then
  Else
    If newVal = "" Then
    Else
      If oldVal = newVal Then
        Target.Value = ""
      Else
        If InStr(oldVal, newVal & ",") Then
          Target.Value = Replace(oldVal, newVal & ",", "")
        Else
          If InStr(oldVal, "," & newVal) Then
            Target.Value = Replace(oldVal, "," & newVal, "")
          Else
            Target.Value = oldVal & "," & newVal
          End If
        End If
      End If
    End If
  End If
End If

exitHandler:
  Application.EnableEvents = True
End Sub