// Get the list of associated doctors
patient.getDoctors(function(err, doctors) {
  // ...
});

// Add entries to the join table
patient.addDoctors([phil, bob], function(err) {
  // ...
});

// Remove existing entries in join table and add new ones
patient.setDoctors([phil, nephewOfBob], function(err) {
  // ...
});

// Checks if patient is associated to specified doctors
patient.hasDoctors([bob], function(err, patientHasBobAsADoctor) {
  // because that is a totally legit and descriptive variable name
  if (patientHasBobAsADoctor) {
    // ...
  } else {
    // ...
  }
});

// Remove specific entries from the join table
patient.removeDoctors([bob], function(err) {
  // ...
});

// And all of the doctor's have their own methods for selecting patients!
bob.getPatients(function(err, patients) {
  if (patients.indexOf(you) !== -1) {
    // woot!
  } else {
    // ...
  }
});

// and so on and so forth

patient.addDoctor(surgeon, {why: 'remove appendix'}, function(err) {
  // ...
});

// or...
surgeon.addPatient(patient, {why: 'remove appendix'}, function(err) {
  // ...
});

Model.hasMany(
  name,       // String. Association name
  otherModel, // Model. The model we're association to
  extraProps, // Object. Extra properties that will appear on the join table
  opts        // Object. Options for the association
);