The evolution and effects of current‐driven instabilities in isothermal, inhomogeneous plasmas are investigated in both theory and experiment. Sucessive destabilizations of four different instabilities, low‐frequency drift wave, ion‐cyclotron drift wave, high‐frequency (continuous‐spectrum ion‐cyclotron) drift wave, and high‐frequency electron wave, are observed inQ‐device plasmas with increased current, and explained by a theory based on fluid and kinetic equations. Anomalous effects resulting from wave‐particle interactions, i.e., enhanced resistivity, ion heating, and electron viscosity, are compared with predictions based on quasi‐linear calculations. Analogous to ion sound causing important anomalies in the transport coefficients for plasmas withTe/Ti≫1, high‐frequency, continuous‐spectrum drift waves determine anomalous plasma behavior in inhomogeneous plasmas withTe/Ti≃1.