HTML datalist元素与PHP的isset结合使用

Question

So I use a datalist element to let my users enter a value. In my PHP code I check if it's set or not and then do some stuff.

Part of my HTML:

<form method="post">
<table style="width: 100%">
<tr>
        <td style="width: 15%">Naam medicament</td>
        <td colspan="5" style="width: 85%">
            <input list="medicament" name="medicament" autocomplete="false">
            <datalist id="medicament" style="width: 50%">
                <?php
                foreach($allMedicament as $medicament) {
                    echo "<option value=\"", $medicament, "\">", $medicament, "</option>" ;
                }
                ?>      
            </datalist>
        </td>
</tr>
</table>
</form>

Part of my PHP:

if (isset($_POST["medicament"])) {
    // this stuff is always executed, even when the user didnt enter or select anything in the datalist
}