  We reveal that a suitable running coupling $\alpha(q^2)$ can reverse the
direction of the one-particle-exchange (OPE) force at long distance if (and
under general assumptions, only if) the exchanged particle has a mass $m$,
either intrinsic or effective. The essential requirement on $\alpha(q^2)$ is an
extrapolating restriction $\alpha (-m^2)<0$. The running of $\alpha(q^2)$ can
be from either renormalization-group evolution or certain derivatives in the
Lagrangian. Reversal of the OPE force direction at long distance (namely,
attraction transits to repulsion, or vice versa) may have important
implications for gravity and cosmic acceleration, particle and nuclear physics,
and also condensed matter properties such as superconductivity.
