Is methotrexate commonly used for psoriatic arthritis?

Methotrexate was originally used in cancer chemotherapy treatments It interferes with the operation of the immune system. It was noted that the use of this drug reduced inflammation in RA sufferers. The amount of methotrexate used to treat RA is far far smaller then that used for chemotherapy and it is still not understood exactly why it has the effect that it has other then it interferes with the immune systems operation. The draw backs in it use are that it can lead to a high degree of toxicity in the system and lead to liver damage if not monitored carefully with regular blood tests. Folic acid is used to help reduce the chance of damage occurring as a result of its use.