Herbal products are rarely covered by insurance and they add up quickly. That cost belongs in the decision, particularly when you cannot be sure the capsule holds what it says.

If you are testing whether a food affects you or your child, the test has to be complete. Among children with suspected sensitivity to artificial colouring, most reacted to as little as 100 mg, so a bit left in is enough to blur the answer.

Before settling on depression as the whole story, ask for thyroid function and vitamin D to be checked. Both are common, both are cheap to test, and an underactive thyroid produces a picture that looks like depression from the outside.

Own brand products from large retailers were among the worst performers in these tests. A big name on the packet is not a quality check, however much it feels like one.