I don't see any errors. I've read it over a few times and really looked, but, I'm not seeing anything wrong. And, sure, there are different ways to write this paragraph, but, I don't see anything wrong with the way it is written right now.
Answer:
The answer for this question will be "unfavorable"
Explanation:
Here, the word adverse means unfavorable. This is because of the fact that if the medication is not taken properly it is likely to affect the health of the living being and may lead to the development of unfavorable symptoms or drastic health complications such as fever and headache.