meto makes SN absorb faster, and you less likely to vomit.
HOWEVER, even without meto, you are very likely to ctb, if you ingest the suggested doses in "exit" handbooks.
Even if you throw up, SN is absorbed very quickly, and without prompt medical help and administration of methylene blue, you would be very likely to ctb. SN is very toxic, in fact most toxic of all azotines (and azotanes as well obviously).
When it comes to supplementary drugs, and you can't get meto - I suggest benzos or opioids (benzos are better option). SN makes your organsm deprived of oxygen, despite not restricting airways and normal breathing. It doesn't cause co2 buildup, but brain trigges a response reaction bc your tissues don't get enough oxygen. This reaction is breathing super heavily and quickly (hyperventilation), "air hunger" (i used " " because it's not "normal" air hunger triggered by co2 buildup, but it's still one), also your heart starts to work super hard, it has to pump blood harder and harder, often leading to sharp chest pain. Besides, you have this panic/terror/feeling of impeding doom, and visible cyanosis (blue color of your fingers) adds to shat.
AAAND - my conclusion is that: This is why I think benzos are even better supplement to SN than meto. Benzos makes you sleepy, dissociated from eniroment, and dull all physical + mental sensations.
Benzo makes sure you won't panic, and call 911, it takes mental terror and physical pain away. All sensations are dulled, hell, if you dose correctly and with correct timing, you could pass out from benzo, and ctb in your sleep from SN.
*NOTE* don't try to ctb on benzos alone. They aren't effective in making you ctb, but are a great supplement to other methods.