There are typically far fewer steps involved when using an auto-injector pen than when using a vial and syringe. Plus, using a pen means you don’t need a separate vial and syringe to take your medication if it’s in a liquid solution.
Also, auto-injector pens may be associated with reduced pain on injection. In the case of subcutaneous methotrexate auto-injector pens, many people have noted they are relatively pain-free to use.
Finally, you and your doctor may prefer an auto-injector pen over a syringe and vial because it can deliver more accurate doses of methotrexate.