I just switched shampoos because I think my scalp is super sensitive to normal shampoo ingredients and was causing some flaking. As far as I know psoriasis is can also be caused by a vitamin D deficiency so start taking some multivitamins and see if that helps.

It is also aggravated by smoking and heavy drinking, as well as stress since it is caused primarily from auto-immune response.

Since Cannabis can act as an immuno-suppressant I see this working for you at least mildly.