Hey, I wouldnt go as far as saying ODs generally dont work. It really depends. Yes overdosing on medications has a pretty high rate of failiure, modern medications are typically designed to be rather safe and potentially dangerous medications are pretty restricted most of the time. But there definitely are medications that can be potentially dangerous and would be relatively reliable in sufficient dosage. You also mentioned nembutal. nembutal, also called pentobarbital, for example is an old sedative-hypnotic drug of the class of barbiturates. There are several barbiturates and theyre all very dangerous and potentially deadly. For example phenobarbital is a barbiturate that is still pretty common, its often used for the treatment of epilepsy and can definitely be lethal. Its far more "accessable" than for example pentobarbital but I also have to say that its far less fat-soluble and has a pretty slow onset of action, ODing on phenobarbital wouldnt be "fast", it could take several hours or more but still, same class as nembutal. There also are other classes of substances which are associated with a pretty high risk for dangerous overdoses, for example opioids. Not only fentanyl, also other strong opioids like oxycodone or morphine can definitely be lethal, especially in combination with other cns depressants. You also mentioned ODing on benzodiazepines and sadly benzodiazepines are pharmacologically known to be very safe, they work as positive allosteric modulators on the GABA-A receptor but have a ceiling effect unlike barbiturates, they can only work with endogenous GABA (which is our most important inhibitory neurotransmitter), thats why benzodiazepines are rarely lethal on their own. The combination with Alcohol is far more dangerous and potentially deadly but even that on its own is pretty "unreliable" when it comes to overdosing in my opinion, it can work but its toxicologically complicated. I would do much research if I was considering a substance overdose and didnt know much about pharmacology, which would be the case for probably most people here. So yes medication overdoses can definitely be lethal but it hugely depends on the substance, and yes pharmacological research would be recommended if anyone considers that as a method but overdoses still carry their own risk factors of course and still are associated with a higher risk of failiure than many other methods. Hope I could help.