About alcohol removing all reasoning, it absolutely does.
However, alcohol won't nessisarily make you "tell the truth", or "say what you wish you could". It lowers inhibitions. So if you had inhibitions about telling the truth then yes, it would help you tell the truth. But among the truths are likely to be piles and piles of shit. If you don't have inhibitions, then your much more likely to say whatever comes to mind (no matter the accuracy.) One could argue that the subconscious mind is telling the truth in that scenario, but I don't think that's quite the case. Drugs like alcohol change perceptions in unique ways, and usually your truths change along with your perceptions.
Here's some neuropharmacology:
Its [ethyl alcohol] effects on GABA-A receptors seem tantalizing, but generally unlikely, due to either a far too high or too low potency, depending on the subunit makeup. Ethanol's inhibition of NMDA receptors seems likely to be a contributor to its effects. The inhibition of AMPA and kainate receptors is too weak to mediate recreational effects, but it may be responsible for ethanol-induced coma. Ethanol's potentiation of alpha7 nicotinic acetylcholine receptors seems a likely cause of some of its rewarding effects, but not a mediator of its general "depressant" character. Ethanol's effects at voltage-gated sodium channels are far too weak to have any effect during recreational usage. BK channel activation might cause some of the effects of ethanol at high concentrations and GIRK channel potentiation could be responsible for its analgesic effects. Potentiation of glycine receptors might cause spinal inhibition and lead to some effects of ethanol, but not the classical cognitive effects. 5-HT3 receptor effects are too weak to mediate ethanol's effects. Inhibition of voltage-gated calcium channels is another likely mediator of ethanol's effects, as it would cause general inhibition of synaptic activity.
http://www.erowid.org/chemicals/alcohol/alcohol_pharmacology1.shtmlAlso, (Central Nervous System) "depressants" is a class with way more than alcohol in it, and they're all different from alcohol.