One solution would be for you to do this control with javascript:
document.querySelectorAll('[name="ReacaoAlergica"]').forEach(function() {
this.addEventListener('click', function() {
div_medicamentos.style.display = ReacaoAlergicaS.checked ? '' : 'none';
});
});
Possui reação alérgica a algum medicamento?
<div>
<input type="radio" id="ReacaoAlergicaS" name="ReacaoAlergica" value="1">
<label for="ReacaoAlergicaS">Sim</label>
<input type="radio" id="ReacaoAlergicaN" name="ReacaoAlergica" value="0">
<label for="ReacaoAlergicaN">Não</label>
</div>
<div id="div_medicamentos" style="display: none">
<label for="quais"> </label>
<select name="medicamentos" >
<option>Escolha o medicamento</option>
<option>A</option>
<option>B</option>
<option>C</option>
</select>
</div>
In the example I first look for elements that have the name equal to ReactionAlergic then I loop these elements to assign a click event, every time one of them is clicked I do a check to see if the yes option is I do not want to be able to do this in any way.
If you have jQuery, the example may decrease slightly:
$('[name="ReacaoAlergica"]').click(function() {
div_medicamentos.style.display = ReacaoAlergicaS.checked ? '' : 'none';
});
NOTE: You should put all the ids and names as I put them in the example, so that the code works correctly.