I've been on accutane for 2.5 months at 40mg a day and my results were SPECTACULAR. I have literally no more acne, my face and body cleared up, and my blackheads were gone. Flat, non-bumpy nose 
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1- In my first month: I was taking 40mg a day in the form of ONE pill only. This was fine and everything went great.
2-I n my second month: I was still taking 40mg a day in the form of ONE pill only. Still progressed and was very happy.
3- In the first half of the 3rd month: I was using accutane which comes in 20mg pills, So I took TWO pills at once every day and things were still fine.
-In the second half of the 3rd month (Currently): I've been taking accutane in the form of 10mg pills, so I've been popping 4 pills at once every day. For some reason, my face started becoming a liiittle oily (it was as dry as the grand canyon), developed a few black heads on my nose, and had a break out of 5 zits. This never happened since i've started my course. Do more pills with less dosage per pill become less potent ? Am I building tolerance ? What is going on here ?!!!! I am definitely upset because I don't want to go back to having acne.
The reason why dosages per pill are different is because I travel A LOT for work, and every country has a different brand with different dosages. FYI the medication in point 2 and 3 is of the same exact brand, just a different dosage per pill, and I've only started developing problems at point 3.
That's what I've been wanting to know too whether the body develops a tolerance for the medication. It's frustrating that I haven't found the answer to this. I doubt the dosage of the pills has anything to do with it since you've been taking a cumulative 40mg per day for almost 4 months now. It wouldn't make a difference what amount the pills had as long as you're getting your 40 in. I think it's time to bump up to a higher dosage now if you're not getting the same results. I think that the body does develop a tolerance for the medication sooner or later and a higher dosage must be taken to keep seeing results. I'm not entirely sure but I think that's the case. Or it could just be a late initial breakout seeing as you didn't have one in the first couple months.