yeah not sure if weight effects it, but start with 200mg. I took about 375mg my first time and it was pretty intense. I weight about 190 or so. I stick to around 350mg now, and it is very enjoyable. Since you seem not to know much about DXM, I strongly advise you to read http://www.third-plateau.org/faq/dxm_faq.shtml

The thing with DXM is there are basically 4 different plateau. The first one is hard to get, and most people go straight to the second plateau. Some say that is the most enjoyable plateau.