According to Wikipedia Robitussin comes in three forms: Robitussin, Robitussin DM which adds DXM and Robitussin CF and contains also a nasal decongestant. None of these seem to be MAOIs, as the regular Robitussin contains Guaifenesin, the DM version contains Guaifenesin and DXM and I can't seem to find the CF ingredients.
DXM is a deliriant as an NMDA receptor antagonist and an SSRI(selective serotonin reuptake inhibitor).
An SSRI is NOT a MAOI, they're two different mechanisms of action. An SSRI functions by preventing serotonin from being removed from the blood by inhibiting the serotonin transporters. MAOIs and RIMAs function by blocking the action of MAO enzymes which degrade serotonin. You can't take an SSRI and expect the action of a MAOI.
Drink an entire bottle of Robitussin will cause a hefty trip. You're better off drinking a cup of Syrian Rue tea than drinking a bottle of DXM contain coughing syrup. Taking DXM in combination with a MAOI could kill you (
source).
The spice extends life.
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