I have been using tretoinon .5% for 18 months every night with no difference. What other type of cream can I try?

Thanks for your question.  All products are not made the same.  Where did you buy it?  Was it over the counter or an internet special?  Your product may have had the described amount of tretoinin, but didn't have a delivery system and it just stayed on the surface instead of soaking into your skin.  Did you only use it at night (it's deactivated by sunlight)?  I suggest you see a physician in your area that specializes in anti aging issues.  Let them recommend products for you.  Best of luck.