My younger son has this and uses nizoral. It works great and there is no down side. We ran out and I didn't immediately replace it and it started right back up. So, it is definitely worth a try.
The answer depends on your personal circumstances. First, the diagnosis of psoriasis might not have been correct. Psoriasis is an autoimmune disorder and is a form of arthritis, and I don't know any cure for it. There are medications out there to control outbreaks. All medications can have side effects, but use of this product on the skin doesn't have too many problems other than causing skin irritation, pimples, and things like that. Orally, it can be liver toxic, but you're not taking it orally. You might find success with gentler products that are more natural, but then again, you might not. You might experiment if you're interested and if they don't work, you can return to this medication. If the flaking stops, stop using the shampoo and see what happens. Your doctor can't predict that and if her diagnosis is right, you have a permanent disease. But it might be wrong, as a lot of docs look at skin problems and say eczema or psoriasis but don't really know for sure. A second opinion with some testing might answer this for you and let you know exactly what you're dealing with, as again, docs often use these terms kind of more colloquially than scientifically, so it wouldn't hurt to as another specialist to confirm is it's really psoriasis you're dealing with. Peace.