I’m using retinol 1%. Why is the strength of my tretinoin prescription so much lower?

Retinols and retinoid acids are similar molecular compounds, but retinoic acid is the ingredient that actually does the heavy lifting. When retinol is applied to the skin, there is a minute conversion of retinol to retinoic acid, which is what makes it effective. Retinoic acids such as tretinoin are already in the active form and are much more potent. In fact, retinoids are at least 20 times (!) more potent than OTC retinols. The number behind the medication is not as important as the medication itself. Tretinoin 0.025% is actually much stronger than retinol 1%. 

The three main retinoids are tretinoin (retin-a), adapalene (differin) and tazarotene (tazorac). But even these medications are different molecules with very different strengths. Adapalene is the weakest in this class, tazarotene is the strongest, with tretinoin in the middle.  Stronger medicines are more effective but increase the likelihood of skin irritation.