While stemming from different sources; addictions, diseases and curses all use the same basic mechanisms. The GM defines a progression of effects (Mild/Strong/Extreme/Deadly), and starts the character off somewhere on the scale. When this is due to an addiction, the character will start out with a Strong effect. In the case of Diseases or Curses, where the character begins is up to the GM, but will usually start at Mild. From this point the symptoms will either get better or worse, dependant on treatment. In the case of Addictions, the symptoms will reduce a stage if the character manages an entire adventure without consuming any of the potions involved in their addiction, and will progress if the character increases their dependence upon alchemy (fulfils the requirements for becoming addicted again). The progression of symptoms for diseases and curses are up to the GM. It is possible for Doctors and Alchemists with the correct skills to treat diseases and addictions. Curses are usually the problem of Mages and Priests, and usually require more inventive treatments.

It is not uncommon for adventures to develop addictions to alchemical preparations. Unfortunately for them, the body rarely knows exactly what it craves, and if they're not careful their addictions can spiral quickly out of control. In mechanical terms, a character is addicted to Alchemy rather than to a specific Alchemical preparation. All characters have a chance of becoming addicted if they drink more than 5 potions in a day (usually represented by the GM flipping a coin). If an addicted character would have become addicted to another potion, they instead find their current addiction to alchemy worsens and in order to go cold turkey they must must refrain from drinking either potion.

While disease is an everyday part of life in the world of Memento Mundi, it is assumed that it is not something characters will often face. While an epic race against time to acquire a rare cure before a village (and yourselves) succumb to a vicious disease is an appropriate focus of an adventure, scouting out a river to ensure there are no dead sheep in it should not form the basis of your average encounter.

Deadly level effects may specify a death condition, although do not have to. Other levels of a progression should not specify a death condition. Although a deadly level effect does not need to have a death condition, the effect should be something that is likely to get a character killed in an encounter (for example: believing friends to be enemies and vice versa), progressing to this level is something to be avoided at all costs.

All of these are examples. GMs should feel free to make up their own progressions, even for those sources that already have an example on the table.