Try a simple search (search engine, BL - posts or threads, Erowid...all great, all yielding many answers to this question). There is no way you have already done the above, because you'd have an answer - or a more specific question if you had. *note, make sure to add necessary details/information in your original post - such as personal drug history, health conditions, experience/s with drug or 'like' drugs, etc. These all help people answer w/ more 'accuracy', otherwise no one can give you decent replies.