How do oral medications and light therapy work?

There are three oral (taken by mouth) medications available in Canada for psoriasis treatment: methotrexate, cyclosporine, and acitretin. They are used for severe psoriasis. Here's how they work:

  • Methotrexate and cyclosporine both belong to a group of medications known as immunosuppressants. They work by decreasing the overall activity of the immune system. Methotrexate may also be given by injection.
  • Acitretin is a synthetic form of vitamin A. It's not understood exactly how it works, but it is believed to slow down cell growth in the skin. It may also decrease skin inflammation and make psoriasis lesions less thick and scaly.

Light therapy is believed to work by decreasing skin cell overgrowth and possibly by decreasing the immune system activity that leads to skin cell overgrowth. It is used for moderate to severe psoriasis. Light therapy is given by a qualified dermatologist, who shines ultraviolet light on the parts of the skin affected by psoriasis (the lesions).

Medications known as psoralens may be used in combination with light therapy to make the skin more sensitive to the light and thus increase the effects of treatment. Unlike oral medications, light therapy can target specific areas of the skin, depending on where the doctor shines the light.

Treatment sessions are usually given several times weekly until the area is cleared. Often, it takes 20 clinic treatment sessions for the therapy to work. There are home equipment options available for phototherapy and may require 40 to 60 sessions since they are less powerful.

Once oral medications or light therapy are stopped, the psoriasis symptoms can return.

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