Magic Fruit

[Catullus64]

In the gardens of the ruined palace of Tanthi, where mighty sorcerer-kings dwelt of old, the green plants still flourish in defiance of the ravages of the desert. Most beautiful of all the trees stands in the center of the courtyard, with golden flowers and grape-sized magenta fruit, and a silver ribbon tied around the base of its trunk. Nature-savvy characters recognize the flowers to be lethally venomous; and yet the fruit is out of keeping with such a plant's usual berries, which are ordinarily small and black. A Detect Magic spell reveals only residual transmutation magic in the ribbon, and an undefined energy in the fruit.

I want the fruit to bolster spellcasting and magic when eaten, but also to be highly addictive, with severe withdrawal symptoms. Any ideas as for benefit/drawback combinations for the fruit? My leading idea is that it recharges expended spell slots, but inflicts the Poisoned condition when those slots are used, until more fruit is eaten; the addiction can only be cured by magic currently beyond the reach of my Level 5 PCs. I also toyed around with the fruit causing hallucinations, but single-player hallucinations are difficult to pull off convincingly at table. Any ideas or past experience on balancing addictive magic-boosting substances?

[Quoz]

You're going to run into some interesting choices since in addition to being highly addictive, these fruits will be quite limited in supply. They can initially harvest something like 20 + the result of a survival check (enough to ensure they get a chance to become addicted) After the initial harvest they grow back slowly, something like 1d10 each week.

Since these berries are sorcerous in origin, giving sorcerer mechanics seems appropriate. When casting a spell, they may consume berries as part of the casting. Each berry gives one sorcery point which must be spent on a metamagic option for that spell (for sorcerers this is doubly potent, as it allows 2 metamagic options on the same spell if they use their own abilities as well)

Whenever berries are consumed, the enhanced spell will always trigger a wild magic surge. Roll one die for each berry used and the player chooses which effect occurs. At the end of any encounter where berries are used, roll a con save to resist addiction, (DC 10 + number of berries consumed that day)

While addicted, every spell cast will trigger a wild magic surge.

While addicted, they will also have the save DC for an spell they cast without using a berry decreased by one.

Once addicted, the caster must consume at least one berry every day or they will go into withdrawal. While in withdrawl the addiction penalties are doubled: -2 to spell saves and all surges roll an additional die; GM chooses which result is worse and uses that.

At the end of a long rest after each day of withdrawl, the addict may make a save to break the addiction (DC 18 - number of days without using a berry). They gain advantage on this save if they have not cast any spells that day. The addiction can also be broken by dispell magic (treat the addiction as a 6th level effect). Remove curse will not clear the addiction, but will count as an additional 2 days of withdrawl and grant an immediate save.