In my opinion, no one should take retinoids until they are past puberty and mature enough mentally and emotionally to evaluate whether or not the benefits are worth risking the side effects. While I haven't taken Soriatane, I've take Accutane and Methotrexate (spelling?) in the past.

On the Accutane my joints ached incredibly, and my depresssion became unbearable.

On the Soriatane, I couldn't eat at all and lost so much weight that I was ordered off it.

Katie is a very positive but rare exception to the rule in that as far as we know, she hasn't had any ill effects. The retinoids are ok when taken for short periods of time (such as to treat acne, which is typically what they are designed for) but for long term use, they can be quite dangerous in that they can cause life long side effects that can inhibit one's physical comfort.
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I am female, and was born in 1972 with Lamellar Ichthyosis.