He does not need opium. He has the gift of reverie.

The line contrasts chemically induced escape (opium) with an innate capacity for imaginative absorption (“reverie”). Nin often treats interior life—dreaming, fantasy, erotic imagination, and artistic contemplation—as a legitimate, even superior, mode of experience. Read this way, the remark praises a person whose mind can generate its own altered states: he can withdraw from the literal world, find pleasure or consolation in daydream, and transform experience through imagination rather than narcotics. It also implies a subtle critique of dependency: the deepest intoxication may come from cultivated sensibility and creative inwardness, not from substances.