An essential amino acid the body cannot make itself, tryptophan is found in protein foods such as oats, seeds and turkey, and the body uses it as a building block when making serotonin and melatonin. This clean, single-ingredient capsule from Viridian is popular with customers looking after their evening routines.

Each vegetarian capsule provides 220mg of free-form L-tryptophan, which needs no digestion before absorption, in a base of alfalfa, spirulina and bilberry. There are no artificial fillers or binders, and the formula meets Viridian's ethical standards, with no GMO ingredients or palm oil. Take one capsule daily away from food, ideally in the evening. Not suitable for children, during pregnancy or breastfeeding, or alongside medication that affects serotonin, such as antidepressants, unless your doctor advises otherwise. The pot holds 30 capsules, a month's supply.