From Learners Dictionary:
Question
What is the difference between preventive and preventative? – Leah, United States
Answer
There is virtually no difference between preventive and preventative. Both words are adjectives that mean, "used to stop something bad from happening." Both words are most often used to talk about health care, in phrases such as these:
Preventive/preventative care
Preventive/preventative health care
Preventive/preventative medicine (a field of medicine)
Preventive/preventative services
Preventive/preventative measures
Finally, both preventive and preventative are used most frequently in academic language and least frequently in fiction.
The one clear difference between the two words is that the shorter one, preventive, is used much more frequently than preventative, possibly three or four times as much, depending on which sources you check.
The bottom line is, you should feel free to use either one of these words to describe something that stops something bad from happening. However, be aware that you may encounter writers, editors, and grammarians who believe that preventive is better, older, and more correct than preventative. None of this is true, but if you want to avoid any conflict, use preventive.
That said, I tend to use "preventative" as a noun- e.g. "Take this as a preventative" which just seems more natural. I tend toward "preventive" as an adjective, e.g. "He is a specialist in preventive medicine".
