Truth serum

A creature subjected to this poison must succeed on a DC 11 Constitution saving throw or become poisoned for 1 hour. The poisoned creature can't knowingly speak a lie, as if under the effect of a zone of truth spell.
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Ingested. A creature must swallow an entire dose of ingested poison to suffer its effects. The dose can be delivered in food or a liquid. You may decide that a partial dose has a reduced effect, such as allowing advantage on the saving throw or dealing only half damage on a failed save.