Theres things called 'plateaus' with the DXM experience, theres four of them and each vary HUGELY, first plateau can be achieved with 100-250mg, this plateau just feels like your body is drunk, theres a slight cognitive alteration, nothing significant though... theres also music euphoria and 'time feels slow' feeling..
Second plateau 300mg -600mg is completly different, you will start to notice that your body is being pulled to the ground, you start having CEV and maybe an OEV or two.. this stage will make your eyes blurry, so forget trying to read anything... this is a nice recreational stage, which i recommend with a nice smoke of ganja at the one hour mark to kick start the disassociative experience... Personally i cant do DXM without weed, it brings out all the psychedelia...
Third Plateau - SHAMANIC, 600mg-900mg... this is not recreational, this stage is for people who want to achieve a true dissassociative state, you WILL experience visions and you will most likely be frightened if your not in the correct mind state... DXM produces a world which is hard to grasp, and with third plateau, you will be very confused..
Fourth Plateau - Commonly known as plateau sigma, COMPLETE SEPERATION OF MIND AND BODY..
for first timers, i recommend no more then 300mg, and keep some ganja around to help improve your trip..
BTW Benadryl dry forte is fucking disgusting, if you think its not bad then there must be something wrong with your mouth..
Robotussin DX which is cherry flavoured, is drinkable... and i find the high to be more euphoric with a less body load..