There are only 3 times that one cannot use wheatgrass.
Grass Allergy
Those with a grass allergy cannot use wheatgrass juice. It is rarely seen but would present as stomach cramping.
Vitamin K Blocker Blood Thinner Users
Like all greens, wheatgrass juice has Vitamin K.
Some blood thinners block Vitamin K and and by introducing additional Vitamin K, it can stop you from achieving your desired INR (international normalized ratio).
If you are using such a blood thinner, your doctor and pharmacist should have instructed you to avoid all green foods including spinach, broccoli, leaf lettuce as well.
Instructed Not To Eat Raw Vegetables
Wheatgrass juice is raw food and contains living componets like naturally occuring ACC bacteria (aerobic colonies counts). In some cases, you may be instructed not to eat raw foods and in this case, wheatgrass juice should be avoided.
