Benadryl (diphenhydramine) and Phenergan (promethazine) are technically the same type of drugs- H1 histamine inhibitors. Benadryl is often listed for its anticholinergic properties as well, but even colloquially people know it as a antihistamine. For example: get a bee sting, elevated histamine response, take a Benadryl. Feel better from an OTC medication.
Promethazine is most often given in the clinical setting for anti-nausea (as listed up-thread) related to post-operative narcotics if the patient has "failed" or lists an aversion to Zofran (Ondansetron) for whatever reason.
It is associated with some unwanted side effects, mainly being tardive dyskinesia (uncontrollable mouth movements), drowsiness, dizziness, confusion, and it's a bit harder on the liver. For this reason, most clinicians will not prescribe promethazine for the patient to take home, but will instead prescribe dissolvable Zofran tablets. It may also cause respiratory depression in high enough doses, which is increased when combined with opiates, which also cause respiratory depression. It wouldn't be unheard of, however, for a clinician to give a patient a take-home prescription if they insisted they could not take Zofran, or if the clinician believed the prescription would be short term.
It's sometimes used in cough syrup preparations because it can suppress coughing as one of its secondary functions.
Where am I going with all this? Because of its sedating effects, those taking it in the syrup preparation paired with codeine came to enjoy it, and that was the origin of "Drank," seen in hiphop subculture in the mid 2010s. Lil Wayne was allegedly hospitalized from it, which is, I think, a preparation of promethazine and codeine syrup, sprite, jolly ranchers and alcohol. You can see how that shit would put you out.
A more "sophisticated" user who could try to just manage drugs as an MBI human, as you noted, might try diphenhydramine and promethazine. Maybe opiates and/or benzodiazepines, maybe MMJ. I don't know their lives. That would certainly, from the effects promethazine and diphenhydramine are known to cause, cause you to feel way out of it. Maybe they're into that.
However, given that both promethazine and diphenhydramine work on the H1 histamine receptor, taking them both at the same time is dangerous. All the bad side effects of antihistamine poisoning? You're going to get there twice as fast. Increased heart rate, nausea, vomiting, loss of balance, possible seizure, coma and even death.
Source:
https://www.latimes.com/science/la-...rp-side-effects-lil-wayne-20130318-story.html
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