Anecdotes are the material for new hypotheses, so they are very much part of the scientific process. This reminds me of the debate around monosodium glutamate

Anecdotes are the material for new hypotheses, so they are very much part of the scientific process. This reminds me of the debate around monosodium glutamate (MSG) causing headaches. There were early scientific reports which found no real link and that it was probably psychosomatic nonsense. However more recent studies found that some people have a heightened sensitivity to glutamate, and since it is a literal neurotransmitter there is a promising pathway for the mechanism of action. Biology is stupendously complex, it's difficult to make hard and fast rules about something being categorically effective or ineffective.