The therapeutic dosage of lithium is close to the toxic level, and dru
gs reducing the renal clearance of lithium can produce the most seriou
s adverse effects. When used in combination with psychiatric drugs aff
ecting mood, the therapeutic potential of lithium may be enhanced, and
earlier concern regarding possible neurotoxic interactions with neuro
leptics appear poorly substantiated. A number of specific interactions
of low incidence have also been reported which should be borne in min
d when new medications are introduced. The ready availability of lithi
um concentration monitoring in body fluids makes it possible to alter
the effects of some potentially interactive drugs that may still need
to be given in combination with lithium.