Yes, constipation can be a big issue with lithium.
Except, anyone in the health field should have been telling you the 11th Commandment:
THOU SHALT DRINK TONS OF FLUID WHILE ON LITHIUM!!
I drink lots. I try to stay away from caffeine as much as possible in pop, but I drink pop, water, juice, tea, even foods like watermelon, cantelope, etc.
I keep a bottle of water by my bed and drink it when I wake up to go to the bathroom at night (another common occurrence while on Lithium).
And I've been on lithium for 20 yrs. The only time I do get into trouble now with constipation is when I'm out of my routine. Like on vacation, or a long shopping day where I haven't stopped for enough breaks.
Yours was a really goood question -
(and by the way, that's been 20 yrs without one single mania or severe depression so think again about avoiding the meds!)