Psoriasis being a constitutional trouble, it requires deep acting genetic constitutional remedy along with other combination medicines. This by acting at genetic level stops the progress of complications of psoriasis and nullifies them completely. Further the medicines work towards impeding the proliferation of skin cells which inevitably alleviates excessive scaling and stimulate the body’s own healing potential by restoring balance of the immune system and countering the genetic predisposition some of commonly used homoeopathic medicines in psoriasis are Graphitis, Natrum Mur, Lycopodium, Sulphar, Sepia, staphysagria, Baryta carb, prosperous, pulsatilla but should be taken under strict medical supervision. 
Psoriasis is an obstinate and chronic disease. There is no shortcut to its cure.The length of treatment varies form case to case, depending of the following factors:

Duration of Psoriasis
Areas affected. Affection of scalp and nails takes longer.
Extent of spread Psoriasis only on skin is easier to treat. Joint affection (Psoriatic Arthritis) require longer duration. 
Previous medication (Extensive use o oral cortisone may delay the course of treatment)
General health and associated diseases