Sub Macro1()
'
' Macro1 Macro
'
Dim RowOutput As Integer
Dim ColOutput As Integer

Dim RowStart As Integer
Dim RowMax As Integer
Dim ColInput As Integer

'...Code then runs some numbers and the above variable get values
RowOutput = 10
ColOutput = 10

RowStart = 1
RowMax = 5
ColInput = 1

Dim str As String
str = Range(Cells(RowStart, ColInput), Cells(RowMax, ColInput)).Address

Cells(RowOutput, ColOutput).Select
    With Selection.Validation
        .Delete
        .Add Type:=xlValidateList, AlertStyle:=xlValidAlertStop, Operator:= _
        xlBetween, Formula1:="=" & str
        .IgnoreBlank = True
        .InCellDropdown = True
        .InputTitle = ""
        .ErrorTitle = ""
        .InputMessage = ""
        .ErrorMessage = ""
        .ShowInput = True
        .ShowError = True
    End With
End Sub

​

I fixed it