How grapefruit juice effects tramadol?

It can potentially increase blood plasma levels of Tramadol if you take more after ingesting grapefruit as it affects/interferes with the metabolism of the drug . So it will not increase the effects of Tramadol that you have already taken but will slow down your liver's ability to break it down leading to higher than normal sustained blood plasma levels. This is not a good thing as drug guidance and dosing information is based on normal metabolism.

You can read about the specific action of grapefruit here: https://www.drugs.com/article/grapefruit-drug-interactions.html