Why does cannabis suppress REM sleep, and does it matter?

THC suppresses REM sleep through CB1 receptor activation in the brainstem reticular formation, particularly the pedunculopontine tegmental (PPT) nucleus, which is critical for REM generation. This reduces both REM duration and density in a dose-dependent manner. Whether this matters clinically is debated. REM sleep is important for emotional memory consolidation and threat extinction — processes relevant to PTSD and anxiety. Chronic REM suppression in animal models impairs fear extinction learning. In humans, long-term heavy users show altered emotional processing. However, for patients whose sleep is severely disrupted by pain or PTSD nightmares, short-term REM suppression may be an acceptable trade-off. Rebound REM (vivid dreams, nightmares) occurs for 1–3 weeks after cessation.