Fentanyl is dangerous, it stops breathing and when your breathing stops eventually your heart will stop due to hypoxia, acidosis, so forth. The DEA states that the lethal dose is about 2mg. To put that into perspective, an example of a dosage that might be used for management of severe pain is around 100mcg, possibly being repeated for continued or cumulative effect. So lethal dose is about x20 the therapeutic dose. This sounds high, but honestly really isn't. Pharmaceuticals are formulated in a concentration intended for therapeutic use, but if you were to find pure, crystalline, powder fentanyl on the market somewhere, it really wouldn't be that much. See the picture below:
The white powder is pure crystalline fentanyl (or at least represents it). Pharmaceutical fentanyl is generally supplied as a solution with a concentration of something like 100mcg (0.1mg)/2mL.
The bottom line is, if you take the lethal dose you will die. The issue that arises is that fentanyl on the market does not come in pure crystalline form. Drug manufacturing and sale would not be profitable if that is how it was sold, as everyone would be fucking dead. When you kill your customers you tend to go out of business.
So, it's very hard to find pure fentanyl. Pharmaceutically it is not supplied that way, and illicitly you would have to go wayyy up the supply chain for that. Of course you could use "street" fentanyl that has been cut with other shit like caffeine, benzodiazepines, mannitol, etc, however at that point it's hard to gauge the concentration and know how much is fatal. Where I live, drug testing organizations only disclose contents and not concentration. They will tell you if a tested drug is pos/neg for fentanyl, but not how much fentanyl is present in the substance by weight or volume.
Best advice would be that if you are going this route, take excess of what you think is needed. Obviously, overdosing is a complicated subject. Many people die of opioid overdose unintentionally, while others try to do it on purpose and fail. In my opinion, this topic should be thought of as a medical procedure as that's essentially what it is. You are giving a specific medication at a specific dose, via a specific route, for a specific purpose... This is no different than giving it for pain, except in this instance the therapeutic dose happens to also be the lethal dose. Just do your research, and consider all methods to decide what is best for you.
I think many people are drawn to fentanyl because it is a painkiller and people have this idea that it will just knock you out and you will have no memory of anything. This is true, but it makes it sound too easy. For it to reliably work, you have to put some thought into the procedure and I feel like (as a suicidal person) planning your own death is anything but relaxing. It's stressful, like any other major life decision.
if quickly reversed with naloxone and with medical treatment
Also... Important to make note of this. Some countries/states/municipalities are distributing naloxone kits. It is one of the safest medications that there is, and there are almost never side effects or adverse reactions at the therapeutic dose. Naloxone has become extremely common and I can guarantee that pretty much every ambulance, cop, and firefighter in the western world probably has it. You have to make sure you are not found or an attempt at resuscitation will be made.
