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The two are often believed to be interchangeable, but the main difference is that retinol is eventually converted into retinoic acid. Retinol is a natural form of vitamin A, while Retin-A is derived from retinoic acid, a synthetic derivative of vitamin A, and considered pharmaceutical.
Benadryl (diphenhydramine) vs. Claritin (loratadine). The main difference between these two medications is that Claritin is a slower acting more long term solution, whereas Benadryl is great for more severe and sudden allergic reactions.