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Having a PC eat a pastry and immediately drop into sleep is a bit sudden for my tastes. I wanted to make the pies a bit more subtle in their execution. In my mind, eating the pies is already like voluntarily failing a wisdom save, so there's no need for PCs to drop where they stand.
The First Taste of Pie
When a player eats a pie, it doesn't effect them right off the bat. You may, if you wish, have them feel a bit drowsy. But it doesn't knock them out.
That night, they have wonderful happy dreams that are so realistic and wonderful, that waking up the next day leaves them feeling hallow. They sleep a full eight hours and cannot be woken while under the influence of the dream pastry.
Addiction Day 1
On the day they wake feeling so sad, by about noon, have the PC roll a DC 10 Con save.
On a success, nothing happens.
On a fail, the PC suddenly finds themselves eating more pie. Don't tell the player that they have to take out the pie and eat it now. Just describe it happening so that the PC feels powerless in the act, much like a real addict might.
If the PC has no more pie on their person or easily available (maybe in another PC's bag or something), they have disadvantage on all their skill checks until they acquire and eat more pie. You may actively tell them they have a hardcore craving for dream pie as well.
If they go to sleep without having eaten dream pie, they have horrible nightmares that night.
Continuing Days After Only Eating Pie ONCE
If a PC has literally only had a single helping of pie ever, the withdrawal will be much easier and shorter than for those who have had multiple helpings over the course of many days.
Addiction Day 1 Happens, but the PC does not eat pie that day. The next day, the PC awakes from horrible nightmares. By noon, have them roll another con save, but with a DC of 4.
On a success, the PC is no longer addicted and is alleviated of their disadvantage if they had any from the previous day.
On a fail, the disadvantage on skill checks continues BUT DOES NOT WORSEN. They will again have nightmares that night, but wake the next day totally free of addiction, disadvantage included.
Becoming Addicted
Addiction Day 2
If the PC ate a second helping of pie during Addiction Day 1, they wake the next day from yet another night of wonderful dreams. At this point, they are addicted. Yes, this is technically only 2 days. But 2 days in-game in dnd can be quite a bit of time, as we're all aware. It's going to feel like longer during actually game play.
By about noon, have them roll another con save, but this time with a DC of 12.
On a success, nothing happens. Their con save the next day will simply go back down to a DC 10 unless they voluntarily eat more pie, in which case it will go up to 12.
On a fail, they once again find themselves suddenly eating more pie. If no pie is available, they have disadvantage on all skill checks until they eat more pie.
Following Days of Addiction After MULTIPLE Helpings of Pie
Each day the PC eats pie, their con save DC the following day will go up by 2, making it harder for them not to feel the effects of their addiction. This can continue to a maximum of DC 25.
Each day the PC goes WITHOUT eating pie, their con save DC the next day will be reduced by 2, to a minimum of 4.
Each day the PC goes without eating pie and is still addicted to pie and fails their con save, they get the following accumulative disadvantages:
Day 1: Disadvantage on all skill checks
Day 2: Disadvantage on all skill checks and saving throws
Day 3: Disadvantage on all skill checks, saving throws, and attack rolls
Eating pie at any point during this time will lift all disadvantages and increase the next day con save DC by 2.
Getting Rid of Addiction
Con Save Success
If a PC doesn't eat pie enough consecutive days, their con save DC will eventually drop to 4. If the PC succeeds on their DC 4 con save, they are no longer addicted.
Going Cold Turkey
If a player goes 7 consecutive in-game days without eating pie, they are no longer addicted. This happens regardless of their save DC amount and immediately alleviates any and all disadvantages they might have had as a result of their addiction.
Relapse
Should a former addict ever eat a Dream Pastry again, their starting con save DC will be 15 instead of 10.
Eating More than One Helping a Day
Eating one pastry in a day or shoveling a whole wagon down in a couple hours does NOT effect addiction levels. The pies work in conjuncture with sleep and dreams, which of course only happens once a day and for a forced eight hour sleeping period. Essentially, a PC has either eaten or not eaten a pastry in-between the times of sleep.
Expiration Date
Due to their magical properties, one dream pastry lasts ten in-game days before expiring and becoming too rancid to eat. If eaten anyway, the player is poisoned for 3 hours due to food poisoning and their addiction level is not effected.