The claim that the priestess at Delphi chewed or burned laurel to induce prophetic trance is repeated constantly and is on much weaker ground than it appears.
What the ancient sources actually support is that the Pythia was associated with the laurel, she is described as holding a laurel branch, the temple was laurel-hung, and Apollo's tree was present throughout the sanctuary. Plutarch, who was a priest at Delphi and is the best-placed witness, discusses the sources of inspiration at some length in the Moralia and attributes the effect to a pneuma, a vapour or exhalation from the ground, and explicitly not to the laurel. He also records that the vapour had weakened over time.
The laurel-chewing detail appears in later and less well-placed sources and has been amplified by modern writers who wanted a pharmacological explanation. There is no known psychoactive constituent of Laurus nobilis that would produce trance at any plausible dose, and attempts to demonstrate one have failed. Chewing bay leaves does very little.
The vapour, interestingly, has partial support. Geological work from the late 1990s onward identified faults intersecting beneath the temple and traces of light hydrocarbon gases including ethylene in the local water and travertine, and ethylene at low concentration does produce a mild euphoric, disinhibited state. That work has been contested on the quantities involved and is not settled. It is a genuinely open question, which is a better description than either the confident chemical explanation or the flat dismissal.