This mod brings back the radiation sickness penalties found in previous Fallout games. It does not undo the changes to Fallout 4's rad system. With this mod rads will lower your maximum health as usual, as well as inflicting Radiation Poisoning if you're irradiated enough.

There are two versions of the mod, one with the Fallout 3/Fallout New Vegas style penalties and one with the SPECIAL penalties found in Fallout, Fallout 2, and Fallout Tactics. There's no extra penalty for reaching 1000 rads, as that's still instantly fatal.

The Fallout 3 Radiation Poisoning stages are:

200 rads - Minor Radiation Poisoning. -1 END.
400 rads - Advanced Radiation Poisoning. -2 END, -1 AGI
600 rads - Critical Radiation Poisoning. -3 END, -2 AGI, -1 STR
800 rads - Deadly Radiation Poisoning. -3 END, -2 AGI, -2 STR

And for old Fallout 1 style stages:

150 rads - Minor Radiation Poisoning. -1 STR
300 rads - Advanced Radiation Poisoning. -1 STR, -1 AGI
450 rads - Critical Radiation Poisoning. -2 STR, -2 AGI, -1 END
600 rads - Deadly Radiation Poisoning. -4 STR, -5 AGI, -3 END. -3 PER, -3 CHR, -1 INT

If you want to change the threshold of each stage, you can use the console to change the global values ThresholdRadPoisonMinor, ThresholdRadPoisonAdvanced, ThresholdRadPoisonCritical, and ThresholdRadPoisonDeadly to whatever you'd like. For example, the command "Set ThresholdRadPoisonCritical to 523" (without quotes) will make you suffer Critical Radiation Poisoning when you reach 523 rads.

Messages will appear in the corner of the screen when you change radiation stages, including when you go from being irradiated any amount to having absolutely no rads, and vice versa.

In terms of hidden mechanics, the mod works by force-feeding the character four silent, invisible 'potions'. This is how Survival mode's needs and diseases work. In this case, the 'potion' effects are always on your character, but only manifest if your rad count is in the proper range. Otherwise, the potions have no effect and do not show on the Pip-Boy. Each potion has an invisible failsafe effect attached to it that will automatically feed the player the potion again if it is somehow dispelled.

I have given these potions the keyword HC_EffectType_Disease so that the effects appear in your HUD as a medical icon. I have given this a quick test and it doesn't seem to cause any issues. I don't know how to edit the interface, so if anyone could help, I would sure like these effects to have a radiation icon instead of a disease icon, if possible. Critical and Deadly stages will show a red icon, just as the more severe stages of hunger and thirst do.

I made this mod to try making a script by myself, and to take a little break from my Better Established Settlements mod. If you are waiting for me to add more to that mod, don't worry, I'll get back to it.

This mod runs a timer checking a relatively simple function every two seconds. I consulted someone with more experience with Papyrus scripts and he said that shouldn't cause any problems. The timer needs to keep restarting itself to keep the script going, so don't worry if you uninstall the mod, the timer should stop after running through one more attempt.

Compatibility:

Doesn't change any vanilla records. Should be compatible with just about everything.

Permissions:

Feel free to incorporate this into/use this for your own mod, as long as you give me credit, don't sell your mod, et cetera... and message me too, please, so I can see what you're working on!

Credits:

ElminsterAU, Hlp, zilav and Sharlikran for FO4Edit
PananaCakes for advising me regarding scripts once again (this time I wrote them all myself, though :) )