Everyone is different, so the same medication will have different effects on individual people. The same goes for methotrexate.
That being said, a medication given through the mouth is absorbed through the stomach and small intestine. When that same medication is given in a different way—say, under the skin—it does not have to go through the stomach and small intestine to be absorbed. This means more of the medication is available to work in the body.
The different ways the drug can be administered may cause a different response in patients. Methotrexate given subcutaneously through an auto-injector pen may be more effective than methotrexate given through a pill—and it may also cause fewer side effects on the stomach.
Subcutaneous methotrexate can be given by injection from a vial and syringe or prefilled syringe or through an auto-injector pen. Auto-injector pens can work in different ways, but they are designed to make it easy for people to inject themselves with a medication.