tobeagenius:

So alcohol induced blackouts- when your memories from the night before are either fragmented or completely gone are caused by a large spike in Blood Alcohol Concentration (BAC). This often happens when we drink large quantities of alcohol very quickly, or if we haven’t eaten much that day- it’s also much more common in females. When our BAC rises quickly, a structure in the brain called the hippocampus is affected.

The hippocampus plays a crucial role in memory. More specifically, it helps the consolidation of information from short-term memory to long term memory. Now when we add alcohol to the mix, our hippocampus can’t do it’s job properly. Information in the short term memory can’t be transferred into your long term memory. So it’s not really a case that alcohol makes you forget, the (long-term) memory is never stored in the first place. 

When alcohol is consumed excessively, more lasting memory problems can be observed. Heavy drinking leads to your body absorbing less vitamin B12 which can cause memory loss symptoms sometimes referred to as ‘alcohol dementia’ which are generally irreversible.