yeah its safe, i would only take one at a time for the first few trips because 500mg will fuck u up nicely, you can take proberbly up to 3 at a time but i wouldnt if i was new to it cause itz extremly intense just slowly work up to higher doses cause the entire trip changes dependant on dose. remember 2000mg is the ld50 for dxm that means half who take that much will die. Also dont do it too much, once a week is more than enough.

otc pills and liquids are a safe source of dxm as long as its the only active ingredient.