Side Effects is a Prepper Stash in Far Cry 5. Prepper Stashes are mini-quests that offer exceptional rewards for completing.
Location[]
Southeast of Hope County Jail at the Bright Warden Radon Spa in Henbane River.
Finding the Stash[]
Look for an entrance to the mines. The note for the stash will be in front of it. Go inside and follow the winding tunnel to the left. Once at the end, there will be a generator. Restart the generator to pull all the Bliss gas out. Players will have to fight their way back to the entrance.
On your way back to the entrance, in the part where there's a large drop in the floor of the walkway and you grapple back to the other side, look to your right to see a short offshoot tunnel. Down that tunnel is minor loot and a safe with money in it. It may be possible to get it on your way in, but it's hard to see with all of the bliss-filled air.
Once back at the entrance, locate a door on the right. The door will now be unlocked and the stash is inside.