Different plasma responses to neutral beam injection in the directions co and counter to the plasma current have long been accepted as wellunderstood in neutral beam heating of tokamak plasmas. Differences can alsooccur in fast wave heating and current drive in the ion cyclotron range offrequencies (ICRF) when antenna arrays are phased to drive current co andcounter to the plasma current. The source of this asymmetry can be easily seenin the cold plasma wave equation with an applied magnetic field in the z direction and the parallel ICRF electric field set to zero (small electronmass limit). In the absence of absorption, the wave equation displays perfectup-down symmetry. However, when absorption is introduced, the up-down symmetryis destroyed by Hall terms, which depend on density and magnetic fieldgradients. This is confirmed by simple numerical solutions of the cold plasmawave equation with and without collisions. The same up-down asymmetry appearsin three dimensional (3-D) antenna coupling calculations with outgoing boundary conditions. These show a natural poloidal shift in the antenna's radiated power spectrum evenwhen no poloidal magnetic field is present. When a poloidal magnetic field isintroduced, the up-down asymmetry acquires a toroidal component. This leads todifferences in electron heating and current drive depending on the directionthat fast waves are launched relative to the plasma current. Such differencesare clearly seen in full wave modelling calculations of heating and currentdrive in NSTX, where poloidal and toroidal magnetic fields are comparable inmagnitude near the antenna. When density gradients are forced to zero, bothup-down and co-counter asymmetries disappear.