TABLE II: Numerical values for the ρ and K ∗ mesons multipoles from several references, computed as stable particles. Reference | ⃗ µ | [ e/ 2 M$_{V}$ ] | X$_{E}$ | [ e/M 2 $_{V}$] [2] ρ : 2+0.26 ρ : 1+0.22 [3] ρ : 2+0.14 ρ : 1+1.65 [4] ρ : 2-0.08 ρ : 1-0.57 [5] ρ : 2+0.01 ρ : 1-1.41 [1] ρ : 2+0.69 ρ : 1+1.8 K ∗ $^{+}$: 2+0.37 K ∗ $^{+}$: 1+0.96 [6] ρ : 2+0.25 ρ : 1-0.75 K ∗ $^{+}$: 2+0.14 K ∗ $^{+}$: 1-0.62 The inclusion of the unstable features of spin-1 particles, without breaking the electro- magnetic gauge invariance, induces a non trivial modification to the electromagnetic vertex of the particle. In this work we have extracted the corresponding modifications to the mul- tipole structure of the W and vector mesons. Our numerical results for the W gauge boson multipoles shows no substantial deviations from the stable case. For the ρ and K ∗ mesons, the mass of the particles in the loop makes a significant effect, pointing out that the unstable nature of the vector mesons can be as relevant as other dynamical effects and should be con- sidered in refinements when accounting for their properties. The modifications in both the propagator and electromagnetic vertex in combination with the Gauge invariance show that the properly defined form factors can be seen as accompanied by a complex renormalization of the vector fields. The general grounds of the loop schemes for spin-1 particles, to account for the finite decay width in a gauge invariant way, have been invoked to study spin-3/2 particles [22]. Since in this case the mass ratio between the unstable particle and the ones in the loop can be very large, further studies are desirable to understand at which extend the finite decay width contributes to the multipoles. IV. CONCLUSIONS 10