DXM does decrease your appetite at high doses, similar to stimulant amphetamine. It also causes insomnia and REM rebound (excessive sleepiness with Rapid Eye Movement). Continuously taking DXM decreases its effectiveness (tolerance). So it’s recommended to intermittently fast (no DXM) for 2 days before indulging yourself on another high dose. However, this approach may cause excessive daytime sleepiness and you might need caffeine to counter that!