No Stupid Questions

Apple seeds contain cyanide, simply crushing them will release the poison and it can be added to something else, although it's not very slow.

There's also the Destroying Angel/Death Cap mushroom, whose symptoms can take up to a day to even start, by which point the toxins have been incorporated and destruction of liver and kidney tissue is irreversible. They also contain toxins that can cause severe DNA damage, making it so your body can no longer repair itself after exposure, and you slowly die cell by cell.

For that i think having a read about acqua tofana would be a pretty good source of inspiration, since it was designed to have effects like an illness. it originates in italy so most of it's ingredients are by default from a mediterran climate.

Or if you want something natural without too mutch human processing, belladonna is a surefire, but not slow acting.

Mistletoe berries i think. Otherwise mercury depending on dosage.

Mushroom poisons usually are slow actors. They take a few days while they kill your liver, and then you'll follow suit.

Time. It's very slow but will get them in the end.

Heavy metals in artists’ oil paints.

You can always dig into true crime, see what methods are used to kill husbands.

Check out ChubbyEmu on YouTube. He’s a pharmacist who presents strange and interesting medical stories (with dramatic re-enactments) involving unusual chemical exposures that damage and sometimes kill people. Examples: soda, coconut water from a bad coconut, a fermented soup, ivermectin ordered online, lab chemicals stolen by a student and given to a disliked roommate, and so on. Maybe something there will inspire you. ChubbyEmu does a good job of breaking down complex medical into an easily digestible format.

Lead, mercury, and other (mostly heavy) metals. Look up mad hatters. Also phosphorus and match girls

well you can try to look it up - slow acting poisons in minecraft.

on a more serious note, as others have noted heavy metal poisoning like mercury or lead.

I have another one - sulphur. Readiy available throughout ancient times, and non-toxic by itself (S8 form that is). But many of it's compounds are toxic in varying degree. You can look its wiki page (https://en.wikipedia.org/wiki/Sulfur) for some commonly available toxic salts, but I also have some ideas to incorporate in story - burning of sulfur (in incomplete form producing SO2 https://en.wikipedia.org/wiki/Sulfur_dioxide). You can incorporate it very easily (someone tampered someone elses fireplace or incense sticks if we also want to hide any wierdities with flame). By itself it iis not very toxic, almost odorless, and not a strong color. It has existed even in food stored for long time due to degradation of sulfur containg organic compounds, wiki page also lists that wine this (another potential vector to supply this). When in body, it can produce H2SO3 (sulphurous acid) and by inhaling/ingesting small amounts for long time - it will gradually destroy alveoli/stomach inner lining and liver. Sulfur by itself is very cheap (you can find ores in a lot of places around the world, relatively easy to mine, also found near volcanic places), humans have used it in trying to make medicine out of it, and it has huge amount of history in alchemy (https://en.wikipedia.org/wiki/Alchemical_symbol, https://www.thoughtco.com/tria-prima-three-primes-of-alchemy-603699). In fact, since it is present in humans naturally, and msot organic matter for that matter - small amount of sulfur being present in someones' reports will not raise a special eye, and they would just be recommended to not eat food that is traditionally know to have much sulfur (for example garlics (https://en.wikipedia.org/wiki/Allyl_isothiocyanate). Garlic extract can also be used to deliver large amount of isothiocynate, but this would be a seperate method of poisoning all together - it is much more lethal, so not very slow acting, but one can keep giving a dose of this below lethal dose to keep damaging liver, and a final blow sometime.

I hope you find this helpful, and I hope no villagers in minecraft are killed by this.

If you want long-term, look to the liver. Alcohol will destroy it over time, but so will viral hepatitis. Have you considered slow acting diseases like hepatitis or HIV? Or something intensely carcinogenic?

There was a theory a while back that Napoleon died from arsenic poisoning due to the damp Mediterranean climate causing the decay of a green wallpaper using an arsenic based dye. It didn't end up being entirely true but he may have been slowly poised by environmental arsenic throughout his life. Here is an article about it.

Arsenic is a naturally occurring element in the Earth's crust as metallic crystals or combined with other elements. Being a heavy metal, arsenic bioaccumulates. That is, it builds up in the body over time, so slow poisoning is possible.

There is a way, and it might already be somewhat of a trope but you can use fruitpits to extract amygdalin which can be then refined with a homelab to a cyanide like substance. Although not pure or concentrated enough, but it could be added to food by a wife on a very long period of time and make the Victim very I'll with fatal results.

Amygdalin is extracted from almonds or apricot kernels by boiling in ethanol; on evaporation of the solution and the addition of diethyl ether, amygdalin is precipitated as white minute crystals.

At work I learned that cyanide is actually very dangerous because it accumulates its effects. Like you have a little now and a little later, then suddenly you can't get up from bed so you call in sick. Its dangerous stuff.

Ricin was used in Breaking Bad. Fairly easy to produce and administer.

don't be Don, don't be Don, don't be Don

Oh thank God.