Table 2.

Recent depletion studies comparing acute tryptophan depletion drink with amino acid balance drink (sham drink) - characteristics and results.

Study	Randomised controlled trial design	Participants: Healthy volunteers (HV) or people with depression*	Medication status	Summary effect (95% CI), p
Frey & McCabe, 2020	Parallel group, double blind	46 HV	No psychotropic medication for at least 3 months	No effect
Bar et al., 2020	Crossover trial, double blind	30 HV	Not specified	No effect
Deza-Araujo et al., 2018	Crossover trial, double blind	85 HV	Not specified	No effect
Martin et al., 2017	Crossover trial, double blind	15 HV	No history of neurological or psychiatric disorders	No effect
Eisner et al., 2016	Crossover trial, double blind	64 HV	No history of neurological or psychiatric disorders	No effect
Trotter et al., 2016	Parallel group, double blind	30 HV	Not specified	No effect
Hogenelst 2016	Crossover trial, double blind	40 HV with or without a family history of MDD	‘No use of psychotropics’	No effect
Weinstein et al., 2015	Crossover trial, double blind	15 people with depression	Treated with sertraline for 12 weeks prior to study	No effect
Moreno et al., 2015	Crossover trial, double blind	64 people with personal and family history of MDD; in remission	No ‘psychotropic medication’ for at least 3 months prior to test	A significant main effect of test condition (χ 2 = 5.14, d.f. = 1, p = 0.023) mainly due to improvement of HDRS scores following sham drink
Hembold et al., 2013	Crossover trial, double blind	18 HV	Not specified	No effect

MDD Major Depressive disorder, HDRS Hamilton depression rating scale.

*sample size has a different meaning in crossover studies since each participant contributes data twice.