The serotonin transporter gene-linked polymorphic region (5-HTTLPR) and the sleep-promoting effects of tryptophan: A randomized placebo-controlled crossover study.

J Psychopharmacol · 2019 · PMC6628462 · PMID 31237183

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hedged sentence

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marginally significantno p-value reported

There was a marginally significant improvement of subjective sleep quality in the 5-HTTLPR S-allele group but not in the L-allele group following tryptophan relative to placebo intake.

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Quoted from the open-access full text in Europe PMC under the licence the publisher applied. The sentence is reproduced exactly as published; the emphasis is ours.