The Surprising Ways THC Can Distort Memory

That Foggy Feeling: Cannabis has a reputation for making things feel a little hazy. But new research out of Washington State University suggests the effect runs deeper than just feeling “out of it.” Even moderate doses of THC may interfere with several different types of memory.

The Study: Researchers recruited 120 regular cannabis users and split them into three double-blind groups. Participants vaped either 20 mg of THC, 40 mg, or a placebo, then completed a series of tests designed to measure seven distinct memory systems over the next hour. The result: THC disrupted nearly all of them. Notably, the 20 mg and 40 mg groups performed similarly, suggesting you don’t need a high dose to see these effects.

The Takeaway: Participants under the influence were more likely to confidently “remember” words they had never actually seen — a phenomenon known as false memory. They also had trouble recalling where information came from (source memory) and struggled with prospective memory — the ability to remember to do something in the future. One exception: their ability to recall past experiences (episodic memory) held up.

Keep in Mind: Research on the short-term cognitive effects of cannabis is still evolving. But these types of memory — remembering tasks, appointments, and responsibilities — are a crucial part of everyday life.