The fact that someone is on many medications will diminish the effects of the oils, but they will still work – results just may be slower.
In answer to a question about using the oils 2 hours apart from medications, the reality is that it may not make any difference as synthetic drugs remain in the body for weeks – or even years. However, it could be more effective to use the oils BEFORE the drugs. That way, the essential oils will have the best opportunity to work in the body with the least interference.
Note: Many therapeutic-grade essential oils absorb into the body within seconds, and all will absorb and begin working within 2-3 minutes – even those with a high molecular weight (the thicker ones).
The key may be in balancing the body enough through the oils that eventually medications may not be necessary.