I have a strong suspicion that creatine accelerated my MPB pre-finasteride. My question is, is it safe to take creatine again now that I’m on finasteride? Will creatine negate the effects of finasteride?
you cannot know it without trying it yourself at the end of the day 
. but I speculate you may slightly up the finasteride’s dosage (eg from 0.5mg to 1mg but not to 5mg, obviously under the guidance of a doctor) and then not much will happen though I don’t know for sure. This is all speculation at the end of the day and I am not a doctor/this is not a medical advice, stay safe.