Can you eat more than one Forbidden Fruit?
The answer is no, you can only eat one. I tested this out on Antica on my noob character because my main world wasn't selling any. I purchased 2 Forbidden Fruits, ate one and it gave me an achievement worth 1 point called "Forbidden Fruit" I wanted to include proof of me testing this out-
"You have now tasted the forbidden fruit. You wonder if this was a good idea. Congratulations! You earned the achievement "Forbidden Fruit".
Now that one of my Forbidden Fruits is gone, I had one left so I tried to use it and it said, "You have tasted enough of the forbidden fruit. More of it might proove hazardous." As you can see there appears to be a typo in "proove" it's supposed to be "prove." I reported this typo to Cipsoft but they said "Maybe it seems like a typo, however, it is written the way we intended it to be written. Since Tibia has a medieval setting some spellings which were common back then are also used in Tibia. Proove is the obsolete spelling of "prove" in the 16th-18th century."
Now it looks like I'll save this fruit for my main!