Pas vraiment d'approche scientifique précise du sujet mais william white y consacre une petite partie dans sa faq
Aller hop copier/coller :
What is the "50 Trip Limit" and How Can I Avoid It?
Recently someone pointed out to me that most of the psychedelic and interesting effects of DXM seemed to go away with repeated use, and hadn't returned. He suggested a limit of about 50 trips; i.e., you get roughly 50 DXM trips before the magic is gone. Other people have said similar things, although the exact number seems to vary from person to person. A few seem to be able to use DXM repeatedly without ever losing the more interesting psychedelic qualitiies.
There are a number of possible explanations for the "50 trip limit". Here are a few I came up with, as well as potential solutions.
1. Long-lasting tolerance. Some people have noticed a tolerance of up to a *year* to the more pleasant effects of DXM. Why this is, I don't know; nor do I know any way to reverse it.
2. Disruption of enzyme systems. It is possible that the P450 enzyme system is disrupted for long periods of time by DXM, although I don't see why this would happen. This could last for quite some time, potentially permanently. It's also possible that a conversion enzyme is *induced* so that the DXM is converted to a metabolite too rapidly. Nothing to be done about this that I know of.
3. State-dependent memory. When you first do DXM, you are in a completely new and wonderful state, and you don't really "integrate" the memories of the non-drug states (including the unpleasantness of drinking cough syrup). As you begin to trip more and more often, environmental cues help you to integrate the drug-state and the non-drug-state. Eventually you will learn to associate the drug not only with the pleasant effects but also with the unpleasantness of taking it, something which doesn't happen early on due to DXM's ability to inhibit memory.
Try taking DXM in a *completely* new environment and see if that changes anything. Make sure to do a *low* dose first, though; if there is a state-dependent tolerance, you could go way too high accidentally if in a new environment.
4. Hallucinogen antidependency. This is a common phenomenon with most psychedelics. After using any psychedelic several dozen times, the magic is gone. It just becomes familiar territory, and with the "wow" factor from the novelty gone, the more mundane aspects (confusion, nausea) of the trip intrude. The solution to this, if there is one, is to put your own "magic" into the experience by interacting with people, trying new experiences, etc. (but don't drive!)
5. Problems with an ingredient in cough syrups. It's possible that the gut, liver, or kidneys start to have trouble metabolizing all the gunk in cough syrups. Try using DXM extract.
6. Age. DXM becomes increasingly less pleasurable as one gets older. No solution that I know of, except possibly to make sure you are physically fit before tripping.
7. Brain damage. I've seen no evidence for this except with very frequent high-dose use (e.g., third or fourth plateau several times a week for several months); furthermore, people who do report DXM becoming less pleasant with time haven't said it's that much faster with high dose trips (whereas any brain damage problem would be). Technically speaking, the damage that Olney et al found with dissociatives is way *beyond* the fourth plateau dosage level, and I'm not convinced that normal users would ever experience it.
8. Cigarettes or other drugs. If you've changed your drug-taking habits, this may affect DXM's effects.
