 [ Symptoms ] i am take synthroid 75 mcgm every day my dr prescribed phentermine 37 5 when should i take each so for best benefit  i am not sure when to take my synthroid and when to take the phentermine so that they do not effect one another [ Disease ] you can really take them at the same time they are totally different mediations the phenteramine is an appetite suppressant so you should take it mid morning to help you with the lunchdinner times the synthroid can be taken anytime