25mg is less than what many companies recomment for slight coughs. 120mg will give you a slight taste. Take 300mgs to feel it nicely, take 900mgs to get absolutly fucked. The best way is to by the Robitussin Cough Gels. Each $8(approx) bottle contains 20 gelcaps containing 15mgs of pure DXM each. So at most $30 will have you tripping hard, probably 4th plateau.