Facing the latest participants attending her four-day psychedelic retreat, Whitney Lasseter made a bold claim: The ceremonies they would take part in were sanctioned by federal law, which sets a high bar for the government to interfere in religious practices.

“We are using these medicines to connect with the divine,” said Ms. Lasseter, the founder of All Tribes Medicine Assembly, one of dozens of organizations that describe themselves as churches and view their use of psychoactive substances as sacramental, even though they are generally illegal under federal law. “It’s your right to practice your religion however you are guided.”

Eight guests seated in a circle in a suburban Austin, Texas, living room nodded, some looking apprehensive, as Ms. Lasseter outlined the sequence of body-jolting, mind-altering rituals ahead.

First, there would be a detoxification protocol in which poisonous secretions of a frog from the Amazon are dabbed on tiny burn marks on a person’s skin, often inducing nausea and projectile vomiting.

Later, they would take a potent dose of psilocybin mushrooms, then smoke toxins from the Sonoran Desert toad, which brings on a brief altered state in which people often flail about, scream and sob. When it is done, many describe a feeling of bliss.

As psychedelics show promise as treatments for depression, trauma and addiction, they are increasingly being offered at retreats that blend spirituality with alternative medicine by people who assert that their dispensing of such compounds is protected under religious freedom laws. There is no official count of psychedelic churches, but an association of them, established two years ago, says it has more than 60 groups in North America.