documentclass[twoside]{article}
usepackage{scrextend}

begin{document}
ifthispageodd{odd}{even}
begin{addmargin}{1pt}
Foo
end{addmargin}
end{document}

LaTeX Warning: Label `1' multiply defined.

relax
new@tpo@label{1}{1}
new@tpo@label{1}{1}