public function commonDrugs()
{
$firm = Firm::model()->findByPk(Yii::app()->session['selected_firm_id']);
$subspecialty_id = $firm->serviceSubspecialtyAssignment->subspecialty_id;
$site_id = Yii::app()->session['selected_site_id'];
$params = array(':subSpecialtyId' => $subspecialty_id, ':siteId' => $site_id);
return Drug::model()->active()->findAll(array('condition' => 'ssd.subspecialty_id = :subSpecialtyId AND ssd.site_id = :siteId', 'join' => 'JOIN site_subspecialty_drug ssd ON ssd.drug_id = t.id', 'order' => 'name', 'params' => $params));
}