Bactra Review    The Lacanian Delusion
There doesn't seem to be any data on the therapeutic effectiveness of Lacanian psychoanalysis in particular, but what there is on psychoanalysis in general does not indicate that it is strikingly more effective than other sorts of psychotherapy, if it isn't actually a bit worse, and all are within striking distance of rates of spontaneous remission. See the (characteristically entertaining) discussion and references in Ernest Gellner, The Psychoanalytic Movement, (2nd. edition, 1995, pp. 197ff)