Method How much dextromethorphan syrup is lethal?

[Dusk till dawn]

As title says

I also would like any references or reports of death cases due to DXM overdose alongside how long it takes for you to die once you take the lethal dose

According to https://www.ncbi.nlm.nih.gov/books/NBK538502/

At doses of 100mg to 300 mg, symptoms ranging from mild stimulation to euphoria and hallucinations can occur. At doses of 300mg to 600mg, dissociation can occur. At doses of 600mg or higher, complete dissociation and coma can occur.

This leads to conclude that for DXM to be lethal, you must ingest at least 600mg

 

[escape_from_hell]

If you consume 600 mg, you will likely just be dissociated and trip for 6-10 hours. Music will sound ethereal. You'll see other places when your eyes are closed.
Other likelihoods include severe diarrhea and nausea on the come-up that may or may not make your puke. Even if you puke, you'll still be high for a long time.

I have taken 600 mg recreationally, I am normal sized person and had no tolerance at the time. It will not kill you. You will probably get a mid 3rd to low 4th plateau experience as described in the online culture of DXM abusers. As far as trips go that was a pretty astonishing and unique one.

If you go to much higher doses, the nausea will almost certainly cause you to throw up, probably even more likely with syrups.
Some people abuse the stuff regularly and take 1+ grams at a time. They definitely suffer cognitively at least in the short term, but even most of them go on to recover to baseline after a couple years.

All that said, it will be nearly impossible to CTB at least orally. Maybe some other creative routes of administration and concomitant substances would help.

Nonetheless, I have thought about using it to sedate myself for CTB. It also numbs physical pain, you might get some bumps and bruises while high you don't notice until later.
This could be helpful for example if you are alone somewhere on a very high bridge, to get high enough to just let go and fall and not be as overwhelmed with panic and pain if at all. For something like drowning it may also work, but you may be having a horrible trip internally in that kind of scenario. It could also work if you found a great spot on the train tracks to chill where you aren't likely to be seen. But you'll get caught easily as your wits won't be about you.

 

[Forveleth]

You can't. It's an over-the-counter medication, which means it's been studied by numerous government agencies and labs and assured to be safe for the general public who may try to drink too much of it. It doesn't matter what papers say. If it was that easy to OD on it, it would not be available to the general public even with a prescription. The best you're going to do is trip balls and the worst you're going to do is put yourself in a lot of pain and severely damage organs. Don't try this.