I accidentally did a very large dose earlier today, because I expected the onset to be a matter of seconds when smoked.
I smoked 3 or 4 4mg doses over maybe 5-6 minutes and was just feeling something very mild. I smoked a 6mg dose right after that. Maybe a minute later, I gave up in disappointment. I went to get a little drink, then walked back to my room so I could weigh a dose of mephedrone. It was right then that it hit me like a ton of bricks. It got even stronger over the next minute or two. I could not figure out what I was doing standing there.
I was very scared, because I was feeling strong bodily sensations. I stayed scared for maybe 10 minutes, fearing that I was suffering brain damage, possibly from a stroke. The fear then diminished. I also realized that I was feeling sound in my body. I also noticed that I could taste sound. I didn't realize the feeling was sound at first because I was just hearing the constant sound of the air conditioner. It became obvious that the feeling was sound when there was a change in sound, though there may be some other component of the physical feeling that isn't sound, but instead a feeling you'd get even in silence. But a big part of the feeling was definitely sound. It was really awesome with music.
My point here though is that it could take a few minutes to kick in. That is not something I expected from smoking it. The drugs I have smoked all kicked in in seconds, before today.
Overdosing due to redosing because of the delay time when smoked, and probably injecting, and maybe for snorting or plugging could be considered a risk for anyone who isn't prepared for it. Maybe this occurs with cannabis too. I still haven't tried weed so I don't know. If it is something that the two drugs share in common, then I would guess people with weed experience would probably know to wait.
I suppose it could be something that only I have experienced, with it kicking in in seconds for everyone else. If so, I have no idea why it tool 10 minutes or longer from my first dose and I guess at least a couple of minutes after the last redose for me to feel much. The time from when I was feeling little to the time when I reached the peak was less than the time from first hit to last hit. It was a very fast ride up. I'd say it hit significantly faster than even an IM injection of ketamine once I started feeling it.
I have no idea how harmful the smoke from this chemical might be. I can say that it doesn't feel harsh or unpleasant. Inhaling the smoke is something I can barely feel at all. That doesn't mean it isn't bad for you, it just doesn't feel like such a bad thing.