My son takes concerta for adhd but loves to drink green tea. will the tea cleanse his system of the medication?

Perhaps, some.: Green tea has significant antioxidants and caffeine in it. Antioxidents speed metabolisim of medications (and toxins) so medication may be metabolized more rapidly. Caffeine stimulates urinary tract activity possibly speeding excretion of medication metabolites. Stimulant meds are metabolized in the liver and excreted by the kidneys. The choice is less caffeine or more medication.

Unlikely: Concerta is broken down by the liver and disposed of by the kidney. Green tea is not known to significantly effect cyp450 )which is what breaks down Concerta in the liver) so it shouldn't break down faster. Green tea can increase urine output but probably not enough to speed up the disposal of concerta, since only a very small amount is disposed of before being broken down.

Not likely: There should not be a problem.