While i dont know too too much on the sublect, i would consider alcohol and DXM to have seperate dangers to consider. Alcohol is more dangerous to the body physically, but DXM, i think, is far more dangerous to your mental health. Both are dirty drugs, which act in completely different ways.
As far as i know, the effects from alcohol come mainly from binding to GABA receptors to act as a central nervous system depressant. pretty straight forward, this would account for it's addictive potential and withdrawal similar to benzodiazepines. (and maybe some interaction with NMDA receptors causing light dissociation)
However, DXM is dirtier, it acts as a serotonin reuptake inhibitor which is more dangerous for those prone to depression, anxiety, and would account for it's longer "recovery" period. similarly to MDMA, some may fall into a bad depression or feel very restless for a long time after regular use is stopped because of a lack of serotonin. for those prone to depression or anxiety, this is something to consider. It even has some light interaction with opioid receptors which could indicate a possibility of a physical dependance. among other things, the dissociative effect comes mainly from its metabolite being an NMDA receptor antagonist. Dissociative drugs in high doses can also trigger psychosis in some.
Based on the usage patterns you stated, DXM bi-monthly is likely less harmful than alcohol, used over than once a week. that being said, it depends on the person and what side effects you would react to. For me, the psychological effects from DXM are definitely more of an issue than any negative effects from alcohol. It may lack the physical dangers and withdrawal periods that alcohol has but DXM is more likely to cause psychological issues.
I enjoy DXM alot more than alcohol, and i don't take either very much myself, but a dose of DXM can negatively affect me for over a week. a dose of alcohol at most will just make me sick.
