Can “additive effects” increase the risk of Stevens-Johnson Syndrome (SJS) with lamotrigine?

Question from a Member (emphasis in red added by us):

Is there an increased risk for Stevens-Johnson Syndrome (SJS) in patients who take allopurinol in addition to lamotrigine?

When I do a drug interaction check, it says that caution is advised because the combination of lamotrigine and allopurinol may increase the risk of CNS depression and psychomotor impairment due to “added effects.”

I did a quick literature review, and all I found was that lamotrigine and allopurinol are 2 of the top 3 meds with risk of Stevens-Johnson Syndrome.