How do stats from chems / aid items stack? How do they add up?

I’ve noticed that chem stacking isn’t as straightforward as I initially imagined. I did the following experiment:

S  P E C I A L
6  5 4 5 6 7 2 -> initial stats without any chem consumption
8  7 6 5 8 7 2 -> buffout + mentats
9 10 7 5 8 7 2 -> buffout + mentats + bufftats
9 13 7 5 8 7 2 -> buffout + mentats + bufftats + orange mentats

So I guess what I’m asking is, what gives? What’s up with that perception outlier?

  • What are the effects of the various Protectron Personality Modes?
  • What Is The Best Weapon (Base Damage Stat)?
  • Do sneak attacks stack with crits?
  • Fallout 4 will not get past the initial loading screen
  • What can I do with stripped Power Armour Frames?
  • Is armor's DR additive and covering whole body?
  • What can I safely store in my workshop?
  • What are the likes and dislikes of the companions?
  • What determines when a location is 'CLEARED' on the map?
  • Is it possible to un-equip power armor frames from NPCs?
  • How to store items safely?
  • How do I change turret targeting parameters?
  • One Solution collect form web for “How do stats from chems / aid items stack? How do they add up?”

    I was only going to post the question but I ended up lifting some weights with my liver for science, and I think I came up with the answer (if someone knows anything else please do tell).

    The answer is:

    1.- There are chem (aka aid items in general) classes. For instance, wine and whiskey are both alcohols, and normal mentats and orange mentats are both mentats. I do not know all chem classes.

    2.- Chems from different classes stack, fully.

    3.- Chems from the same class do the following: if each chem changes different stats, both changes are kept. If the same stat is changed, the effective value is that of the last chem taken, meaning order matters. I don’t know yet if this also affects the length of the effect.

    To illustrate, I’ll show the results of the experiments I made, chems shown in the order I took them:

    Experiment 1:

    Reminder of the effects of chems used:
    Buffout  -> +2 STR, +2 END, +50HP
    Mentats  -> +2 INT, +2 PER
    Bufftats -> +3 STR, +3 END, +3 PER, +65HP
    Orange Mentats -> +5 PER, +10 accuracy in VATS
    
    S  P E C I A L
    6  5 4 5 6 7 2 -> initial stats of my character
    9  8 7 5 6 7 2 -> bufftats
    8  8 6 5 6 7 2 -> bufftats + buffout    (buffout overwrites strength and endurance. Perception from bufftats is kept.)
    8 10 6 5 8 7 2 -> bufftats + buffout + mentats    (bufftats and mentats stack)
    8 13 6 5 8 7 2 -> bufftats + buffout + mentats + orange mentats    (orange tats overwrite mentats but not bufftats, so 5+3. Int from the mentats is kept.)
    8 10 6 5 8 7 2 -> bufftats + buffout + mentats + orange mentats + mentats    (mentats overwrite orange tats)
    

    Experiment 2:

    Beer -> +1 CHR +1 STR -1 INT
    Whiskey -> +2 STR -1 INT
    
    Taking nothing: +0 CHR, +0 STR, +0 INT
    Drinking whiskey: +0 CHR, +2 STR, -1 INT
    Then drinking beer: +1 CHR, +1 STR, -1 INT
    Then whiskey again: +1 CHR, +2 STR, -1 INT
    

    So remember to take your meds in order. I’m off to invest in addictol now.

    We love Playing Games, especially Video Games.