Is wild lettuce safe to use?
In small, properly prepared doses it's traditionally considered safe, but raw plant material and large doses carry real documented toxicity.
The short answer
Raw plant material and excessive doses of wild lettuce have documented toxicity effects including dizziness, nausea, blurred vision, and in more severe cases hallucinations and urinary retention. It should be avoided during pregnancy or breastfeeding, and by anyone with narrow-angle glaucoma, prostate-related urinary retention risk, or a known allergy to Asteraceae-family plants (ragweed, chrysanthemums, marigolds, daisies) — cross-reactivity is a real risk, and patch testing is reasonable first. It also adds to the sedating effect of alcohol, cannabis, and other sedative medications.