The hangover is really a multifactorial condition which includes dehydration as well as toxic chemicals from the breakdown of ethanol which itself is a toxic chemical and inflammation in the body. The best thing I’ve found is multifactorial.
Drink water before you sleep. You can also eat some foods like bread that soak up water so it can absorb more slowly. Also stay up as long as you can to sober up. This is not always possible but if you taper down drinking at the end of the night and hydrate you’ll do better. The final ingredient I’ve found is 800 MG of ibuprofen before sleeping. It makes an amazing difference.