Don't try this brand

There's a shortage of Robitussin, so I ended up getting this brand called Bisolvon. It's got 10mg of DXM per 5 ml & it's 200ml so that's approximately 400mg of DXM

So I drunk the whole bottle like 3 hours ago, I feel a slight feeling of openness & euphoria but it's so underwhelming, I'm not robowalking or anything & now I got diarrhoea, thanks Bisolvon!

I thought I did everything right (no other active ingredients), it's supposed to be a 400mg dose of DXM, any ideas why I'm not tripping?