The short answer
Most advice to "stop" negative self-talk is aimed at the wrong target. Research on thought suppression consistently finds that deliberately trying not to think something tends to increase its frequency, not reduce it. The more workable goal isn't silencing the thought. It's changing your relationship to it.
The research
Deliberately trying not to think about something tends to increase its frequency, not reduce it — a well-documented effect known as ironic process theory.
— Daniel Wegner, 'white bear' experiments, 1987
Why suppression backfires
Wegner's original studies asked participants to specifically avoid thinking about a white bear for five minutes. People instructed to suppress the thought reported it intruding more often than people given no such instruction, and the effect tended to rebound even harder once the suppression attempt ended. The mechanism is thought to involve a kind of built-in monitoring process: to successfully avoid a thought, part of the mind has to keep checking whether it's showing up — which keeps it active rather than letting it fade.
What cognitive defusion does differently
Acceptance and Commitment Therapy (ACT) approaches this from a different angle entirely. Rather than trying to eliminate or argue with a negative thought, its "cognitive defusion" techniques aim to change how much authority the thought carries — treating it as a passing mental event rather than a fact that has to be resolved or obeyed. A recent meta-analysis found ACT produces large effects on repetitive negative thinking and psychological flexibility, though interestingly the same body of research found no significant direct effect on the frequency of automatic thoughts themselves — the thoughts don't necessarily stop showing up. What changes is how much they control behavior and mood once they do.
Metacognitive therapy: a related but distinct approach
Psychologist Adrian Wells's metacognitive therapy research adds a related finding: simply being aware that you're engaging in negative self-talk doesn't, on its own, interrupt it. Awareness needs to be paired with a specific action — something concrete you actually do in response to noticing — or the awareness just becomes one more layer of the same loop ("I know I'm doing this, why can't I stop").
Want to see this pattern in your own thinking, not just in the research?
What this adds up to in practice
Taken together, this research points away from two common but ineffective strategies — suppressing the thought, or simply noticing it and hoping that's enough — and toward something narrower: acknowledge the thought is happening, without engaging with its content, through some small concrete action. That's different from arguing with it (which treats it as a claim worth debating) and different from ignoring it (which the suppression research suggests backfires). A brief, external mark — writing it down, tapping to log it, naming it out loud — tends to occupy that middle ground: acknowledgment without engagement, which is closer to what the research actually supports than either extreme.