Just show them the evidence:

With alternative therapists, when you point out a problem with the evidence, people don’t engage with you about it, or read and reference your work. They get into a huff. They refuse to answer calls or email queries. They wave their hands and mutter sciencey words such as “quantum” and “nano”. They accuse you of being a paid plant from some big pharma conspiracy. They threaten to sue you. They shout, “What about thalidomide, science boy?”, they cry, they call you names, they hold lectures at their trade fairs about how you are a dangerous doctor, they contact and harass your employer, they try to dig up dirt from your personal life, or they actually threaten you with violence (this has all happened to me, and I’m compiling a great collection of stories for a nice documentary, so do keep it coming).