Effective potential including post-Newtonian (PN) and cosmological-constant contributions scaled by the Newtonian potential at the Schwarzschild radius r_s = 2GM/c² versus the radius scaled by r_s. For Λ = 0 (blue curve), stable orbits are reduced to the PN case. For small, perturbative Λ (yellow curve), stable orbits can only become unbounded beyond a certain radius, where the impact of Λ dominates. For large, dominating values of Λ (green curve), there are only unbounded orbits.