Hi Ginny,
Now I'm no expert, I'm sure Dana (Danarx) or Shannon (psychnurse) are much better qualified, but being a user of lithium, I just thought I'd add my thoughts.
Lithium is a mood stabilizer, not just an anti-manic drug. In some cases, bipolar can be controlled with just lithium, but in many cases, as in mine, an anti-depressant is necessary. Does your dad have a psychiatrist? If not I highly recommend that he get one-a family doc is great for controlling depression, but with lithium, a psychiatrist, I feel is your best bet.
Your father should probably be evaluated on how often he is manic or hypomanic versus depressed. Typically if he has a longer history of depressive episodes then he probably needs to be on an anti-depressant. Then again, depending on any other pre-existing health conditions, lithium may be the only medication he can take. He really needs to see his doctor.
Bottom line to remember is this, lithium is meant to stabilize and even out a person's mood, it doesn't always control the onset of a depressive or manic stage it just helps to lessen the frequency.
Hope this helps!
Kelly