L-Theanine - Can a patient with multiple sclerosis use /-theanine without any adverse effects?

Yes, L-theanine is quite good for people with MS. L-theanine has been shown to increase the level of gamma-amino butyric acid (GABA) production, which is important for reducing spasticity, among other MS symptoms. L-theanine crosses the blood brain barrier, this ability allows it to inhibit glutamic acid excitotoxicity, this is the pathological process by which nerve cells are damaged and killed by glutamate and similar substances. Glutamate induced neuro toxicity is a major cause of degenerative brain diseases like Multiple sclerosis, Alzheimer's disease, Amyotrophic lateral sclerosis (ALS), Parkinson's disease and Huntington's disease.

Theanine is the amino acid in green tea, which is also highly recommended for people with MS.

Per Wikipedia, L-Theanin is able to cross the blood-brain barrier, theanine has psychoactive properties.Theanine has been shown to reduce mental and physical stress,and improves cognition and mood in a synergistic manner with caffeine. Which sounds really good for those with MS. Especially those dealing with fatigue and reduce cognition.

However, this supplement also may help the body's immune response to infection by boosting the disease-fighting capacity of gamma delta T cells. Which is a big red flag. People with MS never want to boost their immune system or in other words get their T-cells to become more active than they already are. Such as taking echinacea, which is also on the do not take list for those with MS.

In the end, I would say consult your neurologist/doctor to see if its considered safe for those with MS.