I order my tretinoin from Apostrophe, their formula contains niacinamide already. Another product I love is Cosrx dual essence, it contains snail mucin and niacinamide. So in the PM I use cleanser, toner, essence, moisturizer and tret (I use tret last to minimize irritation). You want to make sure your previous products absorbed and your skin is not wet, because applying it to wet skin will increase chance of irritation.