there are two inputs that should show interactions. Everything works, but when I want to refresh the page I add unset($_SESSION['one'], $_SESSION['second']) an error appears 
Without unset($_SESSION['one'], $_SESSION['second'])
But you still need to reset everything when you refresh the page
search.php
<?php
session_start();
?>
<body>
<form action="new.php" method="post">
<div>
<input type="search" name='search1' list="doc" id="inp1">
<datalist id='doc'>
<option value="diclo">diclo</option>
<option value="keto">keto</option>
</datalist>
</div>
<div>
<input type="search" name='search2' list="doc2" id="inp2">
<datalist id='doc2'>
<option value="diclo">diclo</option>
<option value="keto">keto</option>
</datalist>
</div>
<div>
<button name='btn'>Save</button>
</div>
</form>
<?php
if(isset($_SESSION['error'])) { ?>
<div> <?= $_SESSION['error'] ?></div>
<?php }
unset($_SESSION['error']);
if(isset($_SESSION['one']) && isset($_SESSION['second'])) { ?>
<div>
<div>
<p><?= $_SESSION['one'] ?></p>
</div>
<p><?= $_SESSION['second'] ?></p>
<form action="del.php" method='post'>
<button name='btn1'>INTERACTION</button>
</form>
</div>
<?php }
?>
<?php
if (isset($_SESSION['yes'])) {
$getDrugInt = $model->getDrugInt($_SESSION['one'], $_SESSION['second']);
for ($i = 0; $i < count($getDrugInt); $i++) { ?>
<div>
<p> <?= $getDrugInt[$i]['profDescription']?> </p>
</div>
<?php }
}
unset($_SESSION['yes']);
?>
<?php
unset($_SESSION['one'], $_SESSION['second']); ?>
new.php
session_start();
$arr = array('diclo', 'keto');
if(isset($_POST['btn'])) {
unset($_SESSION['one'], $_SESSION['second']);
$inputone = $_POST['search1'];
$inputsecond = $_POST['search2'];
if(in_array($inputone, $arr) && in_array($inputsecond, $arr)) {
$_SESSION['one'] = $inputone;
$_SESSION['second'] = $inputsecond;
header('location: search.php');
} else {
$_SESSION['error'] = 'No results found';
unset($_SESSION['one'], $_SESSION['second']);
header('location: search.php');
}
}
del.php
session_start();
if(isset($_POST['btn1'])) {
$_SESSION['yes'] = true;
header('location: search.php');
} else {
$_SESSION['yes'] = false;
}
Thank you.