system
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human
What is the mechanism for alcohol dependence?

It seems like alcohol (along with opiates) are rare in that withdrawal can actually cause harm, like seizures or even death.  From what I understand, things like nicotine or cocaine, or caffeine; while not being pleasant aren't going to physically cause you harm if you go cold turkey in basically any case.

My friends and I were talking about this and realized we didn't have any idea what was going on in our brains to cause this type of severe dependency.  Opiates seem to make more sense since the opiates are bonding with specific neurotransmitters; is something similar happening with alcohol?
gpt
Opioids are one of the safest drug classes when it comes to withdrawal.   While withdrawal can be mentally and physically unpleasant, it is not considered unsafe and going cold turkey with just supportive care (i.e. treating symptoms not underlying cause) is almost always a valid option (the notable contraindication being pregnant women).  In fact the first treatment for emergency opioid overdose is an 'anti-opioid' that causes the patient to go through an extreme very fast very painful withdrawal.

Alcohol, benzos, barbituates, and other GABAgeric drugs are commonly considered one of the most dangerous people commonly withdraw from.  Cold turkey is not usually a valid option and a slow tapering plan is almost always prescribed.

As for the neurobiology behind it all...

The pleasurable opioid receptor is the mu-opioid receptor (endogenous compound being endomorphine).  To put it simply, with consistent opioid use the receptors become less sensitive and less endomorphine is created - the defence against feeling physical and mental pain.  With cessation of exogenous opioid use, when one should feel normal pain (i.e. basically no pain), they feel a lot.  The physical withdrawal symptoms are due to the PNS that opioids affect (muscle aches, digestive rapidity) but in the brain it is mostly how one "feels pain" and it isn't dangerous.

GABA is an inhibitory neurotransmitter.  Gabageric drugs (including alcohol) act on GABA or the GABA receptors in different ways - either bind at GABA sites or increasing the amount of GABA in the brain.  With a lot of alcohol use the brain has to get use to acting with more inhibitory neurotransmitter so it learns to act more excited as they dull it down. With cessation of alcohol use the up-regulated GABA receptors in the brain put it into a hyper excited state which can lead to seizures, delrium, and death.

edit:

tldr regarding the CNS;

Opioids make you feel good, you get used to feeling good i.e. feel normal, now stopping them doesn't make you feel normal but you feel bad.

Alcohol slows down your brain, your brian gets used to being slowed down by going fast so it cancels out and it acts normal, stopping it makes your brain go super fast possibly killing you.