Weight is my go to for any measurement I want to be reasonably precise, solids or liquids. my kitchen scale gets a lot of use.
that said, if this is a baked good like a cookie or brownie where you enjoy biting into the existing texture, I’d probably go with less precise and just cutting it by eye in whatever way seems less destructive. 1/5ths is a little tough though. I’d tend to go for 1/4 or 1/6 and feel better about the precision to cut something in half and then half again or in thirds and then half again.
It’s often not so simple as a person making a choice and knowing the outcome. There are often many tragic factors that contribute to the situation that resulted in the overdose. One common situation is someone is injured and prescribed opioids by their doctor, perhaps having been influenced by drug companies like Purdue pharma. As they take it they become addicted, eventually the doctor cuts them off and they go to other doctors, then they may find it easier to buy from a dealer, then they may find it more affordable to buy fentanyl, and then maybe they take too much or get a bad batch and od.
They didn’t start taking drugs knowing it was going to be a bad path, they started because their doctor prescribed it and by the time they figured out they were addicted they were no longer in control and may not have had the resources to get out. It’s often not just a question of willpower but one of support and resources to help you up.
There are many other scenarios, but it’s rarely a simple result of a few conscious choices and almost always a result of people suffering in bad situations and it’s ok to feel compassion and empathy even if they weren’t completely innocent in it all.