  Scalars and pseudoscalars with masses in the MeV to GeV range are of interest
in different extensions of the Standard Model. Such particles are often
associated with dark matter, the strong CP problem and the
$\left(g-2\right)_{\mu}$ anomaly. In this work we investigate limits for masses
of such particles and their couplings to photons and leptons which can be
derived from present and future $e^+e^-$ collider experiments and current
$\left(g-2\right)_{l}$ measurements. Our work expands upon previous studies in
several ways, demonstrating that the interplay of both couplings is a decisive
factor in this type of analyses.
