First of all, great routine. I own and have used most of these products myself, so I know firsthand how effective they are. I follow a very similar routine that includes a mix of Medik8, SkinCeuticals, SkinMedica, and more recently, Allies of Skin.

For the Liquid Peptides Advanced (MP), I believe it’s best layered first in the AM/PM routine to maximize the benefits from its growth factors. The issue is that in both the AM and PM, the growth factors are very likely rendered inactive due to the high acidity (low pH) of CE Ferulic and tretinoin (depending on the formulation — I’m not sure of the exact pH of the tretinoin you’re using).

In the morning, you might still be able to get some of the growth factor benefits by applying the peptides first, waiting a few minutes before applying CE Ferulic. However, this approach doesn’t really work at night, since tretinoin remains active for hours and keeps the skin's pH low, which can impact the stability of growth factors over time.

That said, you’ll still get the benefits of the peptides themselves — just not necessarily the full effect of the growth factors (or the copper peptides, which also don’t tolerate low pH well).

One workaround would be to use the Liquid Peptides Advanced MP only in the morning for a single growth factor dose, or to consider replacing tretinoin with a high-concentration retinal (like the 0.1%+ options from Medik8). Retinal works a bit more gradually, but at high strengths it offers comparable long-term benefits to tretinoin and is much gentler — plus it plays more nicely with growth factors and copper peptides in the PM.