Laravel ajax post(Can't find ajax request)

I'm trying to send ajax request in laravel 5.1. but i can't get ajax request. it always HTTP request.

I have a html form

<form role="form" method="POST" action="/admin/save-drug" id="add_drug">

<label for="drugs_name">Drug Name <span class="text-danger">*</span></label>
<input type="text" class="form-control" name="drugs_name" id="drugs_name">

<label for="drugs_name">Drug Name <span class="text-danger">*</span></label>
<input type="text" class="form-control" name="drugs_name" id="drugs_name">

<button type="submit" id="save_drug" class="btn btn-default waves-effect waves-light btn-md">
</form>

And i use ajax

$(document).ready(function(){
            $('#add_drug').submit(function  (){
                $.ajax({
                    url: './admin/save-drug',
                    type: 'POST',
                    data : { 'drugs_name':$('input[name=drugs_name]').val()},

                        success: function(data){
                            alert(data)
                        }
                });
            });
        });

My Controller

public function saveDrug(Request $request){
        if($request->ajax()){
            return "AJAX";
        }else{
            return "HTTP";
        }
    }

It alwayes return "HTTP" what's wrong with my code???

via Chebli Mohamed