I have an earache:

2000 B.C. - Here, eat this root.

1000 A.D. - That root is heathen, say this prayer.

1850 A.D. - That prayer is superstition, drink this potion.

1940 A.D. - That potion is snake oil, swallow this pill.

1985 A.D. - That pill is ineffective, take this antibiotic.

2009 A.D. - That antibiotic is artificial. Here, eat this root.