I've heard mixed responses about this actually. Most of what I've read though seems to say that you can apply moisturizer at the same time. I know personally for myself, I've been moisturizing in the morning and night and I'm at the 11 week mark. I notice if I don't moisturize at night and let it go for a few days my skin starts to just look more dull and gets really dry and the minute I start to moisturize more it starts to plump up and look better, more healthy. Justa few days ago I tried to not moisturize at night and noticed this after a few days. That being said, I think maybe it depends on how your skin is as well. I'm more prone to dryness and irritation so it's usually a must that I moisturize, especially with the drying effect of retin-a.

So, after all that, I think it's safe to assume that a gentle moisturizer like Cetaphil or what-have-you is perfectly fine and shouldn't have any affect on the retin a. What I do though, is wait at least 30 minutes after I apply my retin-a before I moisturize, just so that I know the retin- a is fully absorbed and to prevent any possible irritation. I just wouldn't moisturize with anything that has any kind of ingredients like alpha hydroxy acids or SA, or anything that can further irritate your skin while on retin-a or can cancel out the retin-a. So, yeah, normal moisturizers with no crazy ingredients should be fine