Lithium for manic depression 1200mg?

In my experience, taking lithium capsules spread over the day is easier to tolerate. They do come in 150mg to 300mg so you can spread them, maybe taking a larger dose before going to bed. Also, drinking a lot of water and eating before taking each capsule may help your stomach.

Usual Adult Dose for Bipolar Disorder
Acute Control: 1800 mg/day
-Regular release formulations: 600 mg orally 2 to 3 times a day
-Extended release formulations: 900 mg orally 2 times a day

Long-term Control: 900 to 1200 mg/day
-Regular release formulations: 300 to 600 mg orally 2 to 3 times a day
-Extended release formulations: 600 mg orally 2 times a day

Comments:
-Regular release formulations should be given in the morning, afternoon, and nighttime (3 times a day dosing) or in the morning and at nighttime (2 times a day dosing).
-Extended release formulations should be given in the morning and at nighttime.
-Dosing must be individualized according to serum levels and the response to treatment.
-Alternative extended release formulation doses are 600 mg 3 times a day (acute control) and 300 mg 3 to 4 times a day (long-term control).

Uses:
-Treatment of manic episodes of bipolar disorder
-Maintenance treatment for individuals with bipolar disorder

Source: https://www.drugs.com/dosage/lithium.html#Usual_Adult_Dose_for_Bipolar_Disorder