Side effects and ways to combat them:
1. itch. the first time i tried dxm, i took 700 mg of pure powder,(WAY too much, not recommended) and while the trip itsself was extremely interesting, the itch was annoying, burning, painful, and generally a buzzkill. i have since taken dxm around 20-30 times, and there is only 1 thing that totally gets rid of ALL itching or unpleasant body effects. BENADRYL. take 2-3 25 mg tabs of benadryl right after you dose, and although this is obviously subjective, it works wonders for me.
2. nausea. again, benadryl. this unpleasantly sedating antihistamine on its own just does wonders for my dxm trips. no nausea, no itch, no negative effects whatsoever. marijuana is also great for both itching and nausea, but dont pack a bowl unless you feel like jumping a plateau. i enjoy cannabis much more on its own or with the more "traditional" psychedelics.
3. heat flashes. there really isnt a way to combat this, but as long as you know you arent lacking any enzymes(sp?) and have taken a "safe" dose, there really isnt anything to worry about in my opinion. getting paranoid over the heat flashes increases them 10 fold, and basically ruins the trip for me. just relax, turn the air conditioner on, put on some good music,(aphex twin being my favorite for dxm trips) and let your mind flow. pretend your body doesnt exist.(well, its not going to anyway at high dosages!)
The first few times i tried dxm, i HATED it, thought it was the most disgusting drug out there, and vowed never to do it again. Of course, curiousity got the best of me, and i tried it again, this time trying to aim for a 1st plateau dose, around 170 mgs of powder. I loved the euphoric, but mild effects, and started to increase dosage slightly every time i used dxm again, which was usually once every 2-3 weeks. Also, with the benadryl or a small amount of cannabis, i experience no negative side effects, no hangover, just pure fun dxm strangeness at its best, even when i used robitussin max strength when i couldnt get powder. Since i started gradually increasing dosages, my trips have all been very interesting, along with general euphoria. Moderation is key just like any other substance.
One last note;I DO NOT RECOMMEND using DXM as a substitute for other drugs, especially as a pleasure drug when out of marijuana/whatever your "pleasure" drug is. Disorienting, horrifying, and generally disgusting experiences often occur when naive kids try to use DXM to just get "fucked up". treat it just like other strong psychoactives, not as a desperation drug. dxm is a "real" drug, and imo a good change from the more traditional psychedelics. Just be patient, have some pot or benadryl on hand, and enjoy, if your body can handle it. I love disassociatives, namely ketamine, but lately k has been totally non-existant in my area, and ive tried pcp on several different occaisions, i just never really enjoyed how it made me feel. I may even go as far as to say i like dxm more than ketamine, just because of the longer duration, and the wider range of effects(ketamine is still more intense imo) and the fact that i dont really get any negative effects from dxm, just a pleasant afterglow and maybe feeling a bit tired the next morning.