Currently there are only a few creams that are prescribed and...

Currently there are only a few creams that are prescribed and some what effective for psoriasis.
One of them is a vitamin D steroid cream that thins the skin quite severely with prolonged use and once you stop using it the condition comes back worse than before, it's also quite expensive at around $45 for a 30g tube.

Depending on how bad your psoriasis is this will only last about a month. I've actually stopped using this cream because of how bad it gets after I stop using it, I now use less effective moisturisers. It's a terrible condition that most doctors struggle to treat.

There is medications like biologics that are reported to be very effective but they also have more side affects, I personally haven't tried any.