I'm note sure I follow your logic. Are you saying that if you can't give specific, alternative explanations for the missing car, we must consider aliens a plausible explanation?
We know that there are foods that have medical benefit. There are foods that contain anti-histamine capabilities, for example, or decongestant capabilities that could have been positively impactful on hay fever. These may have been a part of OP's dietary supplements.
Without knowing what the supplements were, we cannot dismiss that they might possibly have been of aid.
I mean sure it could have been stolen, or towed, or aliens, etc. But, the point is when what happens can have reasonable explanations it's not evidence for ET.
PS: And no I would not take those odds even though it may have helped, there are odds vastly below 1%.