Is taking 50,000 ui vitamin d twice a day for one month, safe? my doctor told me to do this. side question (is it alright to take it while on ssri?)

That's a HUGE dose: People usually take 400, 800, 1000, or 2000 units of vitamin D each day. For people who have very low levels of vitamin D, they can take 50,000 units once a week for some weeks (to store up a bunch of vitamin D in their bodies) and then switch back to perhaps 2000 units each day. Haven't heard of people using the 50,000 unit tablets more than once a week.