I believe the issue with taking Glutathione orally is that it is considered very difficult to absorb. You will find references like this:
As demonstrated in several earlier studies, oral administration of glutathione does not lead to high enough serum concentration to be of any therapeutic value at all due to extremely poor absorption from the gastrointestinal tract.
This is why the option of IV talked about. Some oral forms of it claim to be more absorbable than others.