can i take 2 50mg tablets, instead of one 100mg tablet of pristiq?

Hi mi.man,
This is a question that only your prescribing doctor can answer, as s/he will need to re-write your prescription with updated information about how to take your medication.

If your prescribing doctor has updated your prescription that you need to take 100mg of medication in the form of (2) 50mg tablets, the prescription also needs to specify how and when you are to take this medication. (For example: take (2) 50mg tablets at bedtime; take (2) 50mg per day, 1 in evening and 1 in morning....there are many different ways the prescription can be written)).

Please contact your prescribing doctor, and inquire about a newly written prescription, so that you can take your medication most effectively.