TCPR: How do you know if a belief is a delusion? 
Dr. Pierre: It’s tricky. Delusions are defined as fixed, false beliefs, but that definition isn’t always useful in practice since many beliefs aren’t falsifiable. We can instead look at how plausible or “bizarre” a belief is, but that can also be problematic. Whether you think something is plausible depends on your worldview. Historically, psychiatrists have viewed bizarre delusions as a sign of schizophrenia whereas non-bizarre delusions are typical of delusional disorder. But when psychiatrists are asked to rate bizarreness, the inter-rater reliability is very low, so the term has been largely abandoned (Bell V et al, Schizophr Res 2006;86(1–3):76–79).

TCPR: What if a patient says God speaks to them?
Dr. Pierre: For someone with certain religious beliefs, that might be considered plausible. Another person might believe we live in a multiverse with infinite copies of ourselves inhabiting other universes—some physicists even agree that’s possible! So, there are often challenges to assessment based on the content of a delusion, particularly in a multicultural society. That’s why I often find it more helpful to assess belief on a continuum rather than as an all-or-nothing phenomenon.

TCPR: So, you’re judging the probability that a patient’s belief is a delusion?
Dr. Pierre: Yes. I think of delusionality as a matter of degree where pathology isn’t so much based on what someone believes, but how they believe it. I look at conviction, preoccupation, action, and emotional investment. For example, lots of people say they believe in angels or aliens, but they don’t think about it all day. They don’t feel passionate about it. They don’t act on it. When pressed, they admit they aren’t sure. I wouldn’t consider that delusional. But if they’re convinced, can’t stop thinking about it, and feel compelled to do something about it, that’s more in line with a delusion.

“Pathology isn’t so much about what someone believes, but how they believe it.”

Joseph Pierre, MD

TCPR: I want to raise a challenge. In 2016, a man drove from North Carolina and fired shots at the Comet Ping Pong pizzeria in Washington, DC. He was driven by a conspiracy theory that politicians were running a pedophilia ring out of the restaurant. He was full of conviction and emotional investment, and he took action, but he did not have psychosis (as far as we know).
Dr. Pierre: Yes, assessing delusions isn’t easy! His case illustrates another key feature of delusions: self-referentiality. We see this in psychotic disorders where the delusions are all about the person. They might believe that people are targeting them, spying on them, talking about them. Conspiracy theories are less about the believer and more about the world, whether it’s aliens, celebrities, or what governments are up to behind closed doors. In the case you brought up, he had read about the “Pizzagate” conspiracy theory on the internet. He couldn’t get the idea that children might be in danger out of his head. It deeply concerned him as a Christian and a father. But he didn’t feel that he was being targeted. He was motivated to save the kids. I call that “self-relevant consequentiality.” In contrast, patients with paranoid delusions tend to take action to protect themselves when they feel that they’re in danger. That’s self-referentiality.

TCPR: I suppose it’s also plausible that powerful people are involved in pedophilia.
Dr. Pierre: Many would agree with you. And that shareability also points away from delusional thinking. That’s why conspiracy theories about the world spread so easily, while the beliefs of a person with schizophrenia stay more isolated. Self-referential ideas are much less likely to be viewed as plausible or likely. 

TCPR: What is an “overvalued idea”? 
Dr. Pierre: That’s a term the DSM uses for rigid beliefs that don’t rise to the level of a delusion. The DSM focuses on the strength of the belief. An overvalued idea is “maintained with less than delusional intensity,” and the DSM states that “the person is able to acknowledge the possibility that the belief may not be true.” However, the DSM goes on to say that overvalued ideas are “not ordinarily accepted by other members of the person’s culture or subculture,” so conspiracy theories may not fit there. That’s another tricky aspect of assessing delusions—now that the internet has given us easier access to other like-minded individuals, shareability has changed. These days, it’s not hard to find a subculture that supports even the most fringe beliefs.

TCPR: Sometimes people with psychosis get caught up in conspiracy theories, making the diagnosis even more confusing.
Dr. Pierre: Yes. One theory about delusions is that they arise out of unusual subjective experiences. Later, the patient adopts a belief system to explain it, often pulling from what’s already out there in the culture. In the 1800s, if someone heard a voice when they were alone, they might think it was an angel or a demon. Today, they might explain it in terms of radio frequencies, implanted devices, or “voice to skull” technology. 

TCPR: What is that? 
Dr. Pierre: It comes from a popular belief called “gangstalking.” The idea is that governments, law enforcement agencies, or other bad actors are running a kind of worldwide surveillance program. Their intent is not just to spy, but to single people out and harass them with “voice to skull technology,” “microwave attacks,” “psychotronic weapons,” or even hypnotic suggestion. Essentially, they’re setting out to make people crazy. 

TCPR: That sounds like something I read in the mainstream news. It was a possible explanation for an illness that struck the US embassy in Havana, Cuba.
Dr. Pierre: Yes, that’s an example of how conspiracy theories and delusions can overlap. On the one hand, there have been congressional hearings about “Havana syndrome,” with some government officials arguing it was caused by a sonic microwave attack. But on the other hand, some people take that unsubstantiated conjecture as evidence to support their own self-referential paranoia. As many as 1 in 250 people believe in gangstalking, and there are support groups for those who think it’s the cause of unexplained symptoms like dizziness, headaches, or even voice-hearing and ideas of reference (Sheridan L et al, Int J Environ Res Public Health 2020;17(7):2506).

TCPR: Did they ever find the cause of the original problem in Havana? 
Dr. Pierre: Not yet. The story actually dates back to the 1950s, when people developed similar symptoms at the US Embassy in Moscow. There was a long-standing belief that the Russians were using microwaves to attack American embassy staff. But like Havana syndrome, that was never proven. And some have theorized that the occurrences in both Moscow and Havana might be better explained by mass psychogenic illness (Bartholomew R et al, Int J Soc Psychiatr 2023;70(2):402–405).

TCPR: Do you see more conspiracy theories in autistic patients?
Dr. Pierre: Autistic people often have idiosyncratic beliefs, and they may be more prone to such beliefs because they don’t socialize like others do. Another feature of autism spectrum disorder is cognitive rigidity—they can be dogmatic. Taken together, these factors can make it difficult to tease out rigid, autistic thinking from delusional beliefs. The two aren’t mutually exclusive, though. People with autism can have psychosis. And again, it might be a matter of degree.

TCPR: How does a patient’s stimulant use influence your assessment of delusions? 
Dr. Pierre: Of course, we know that drugs like cocaine or methamphetamines can cause psychosis. But we used to think that prescription stimulants didn’t elevate the risk of psychosis much at therapeutic doses. Recent studies have changed that view, particularly with amphetamines, which have twice the risk compared to methylphenidate (Moran LV et al, N Engl J Med 2019;380(12):1128–1138). We’re also seeing psychosis more when combined with cannabis or other drugs like psychedelics. So, if I see delusional thinking in that context, I’m going to first focus on getting someone off the potentially offending agent to see if the delusional thinking resolves. There’s little justification to continue prescribing stimulants in someone with active psychosis. 

TCPR: Are today’s conspiracy theories different from those of the past?
Dr. Pierre: Conspiracy theories have been around forever. But today, people have more access to information—and misinformation—and they’re often more socially isolated, so that’s changing how the theories spread. Many modern theories are also more consequential. In the past, if you believed that there was a UFO crash at Roswell or that Princess Diana was murdered, so what? But now, if people believe that climate change is a hoax or that the government is hiding the harms of vaccines, that can have real consequences—like vaccine hesitancy leading to the worst outbreak of measles in 30 years.

TCPR: How do you keep up with all these new beliefs?
Dr. Pierre: It’s hard, since there’s almost no limit to what’s out there. Here’s a tip. When you hear someone mention an unusual belief, ask them, “What makes you believe this?” If it’s a conspiracy theory, they’ll likely trace it back to a website or a YouTube video. A few years ago, there was a popular video that claimed to offer “200 proofs that the Earth is not a spinning ball,” and a lot of “flat Earthers” cited it as evidence. In the old days, if you told your friends about such things, they’d probably call you crazy. But today we can find support for just about anything on the internet. Some beliefs have become mainstream and even official narratives. Lizard people running the government, UFO cover-ups, chemtrails, gangstalking, Jewish space lasers causing fires, cloud seeding being used to control the weather or cause hurricanes—you name it.

TCPR: Do you Google your patients’ beliefs?
Dr. Pierre: For sure. Ten years ago, I admitted a young man for methamphetamine use disorder. His main symptom was a belief in government conspiracies. When I asked why he believed the conspiracies he’d mentioned, he said, “Dude, you gotta go on Alex Jones’ site, Infowars.” I looked, and sure enough, it was all there. It wasn’t a delusion. He was just parroting stuff he read online. That was before I knew what Infowars was, so without checking, I wouldn’t have known.

TCPR: What do we know about people who are drawn to conspiracy theories? 
Dr. Pierre: There’s been a lot of research into this. People who believe in conspiracies aren’t unintelligent, contrary to what is often claimed. But there are a lot of other correlates, like needs for control, closure, and certainty—or uniqueness. The framework I like to emphasize involves mistrust, misinformation, and motivated reasoning.

TCPR: Walk us through those.
Dr. Pierre: When people don’t trust mainstream information, they go searching for alternative sources. In today’s world, that easily leads us to misinformation, because that’s often what grabs our attention on the internet and on social media. And when we engage with such information, we often do so using motivated reasoning. In other words, we celebrate sources that confirm our existing beliefs or intuitions, and dismiss findings that contradict them. Some research has found that people with higher intelligence or more education may be particularly prone to motivated reasoning. Why? Because critical thinking skills can make you adept at dismissing the findings you disagree with.

TCPR: What about needs for certainty or uniqueness?
Dr. Pierre: Conspiracy theories may be appealing because they offer tidy explanations during times of crisis and uncertainty. And then there’s the feeling that a conspiracy theory believer has discovered the real truth whereas everyone else is blind—they’re the “sheeple.” That can be empowering, and that feeling of specialness can be hard to give up.

TCPR: Sounds like conspiracy theory believers are often more normal than not.
Dr. Pierre: Exactly. We all have needs for uniqueness, belonging, and closure. These aren’t inherently psychopathological traits. Some people have stronger traits than others, but surveys consistently find that most people believe in at least one conspiracy theory. So, unlike delusional thinking, it’s a totally normal phenomenon.

TCPR: Thank you for your time, Dr. Pierre.