These products are generally cheaper than the better-known brands and are almost identical.
Take milk for example. Woolworths and Coles don't have their own dairy but they have their own brand of milk. They do this by approaching existing dairies and asking them to provide milk in a Coles or Woolworths branded bottle.
This also applies to medications as well. The active ingredient in generic medications will remain the same.
The generic store brand version of Panadol still contains the active ingredient paracetamol. The same is true with Nurofen and the active ingredient, ibuprofen.
Of course, some of the other ingredients can vary so if you have any allergies or concerns with medications then consult a pharmacist or GP.
When you buy branded products, typically you are paying more for a fancier packet.