The deepweb is an option or you should be well connected by someone to get some medicines for bitcoin, its possible for sure.
Yes possible for those illegal medicines/drugs but for those what OP wants is also available in deepweb but its not advisable to buy in that place, you must take the risk before going there.
The problem with buying medicine in the deep web is you don't know what someone is selling to you, may be it is not what you thought it was, maybe the medicine was adulterated in some way or form and you will never know that.