Buddhism holds that physical suffering and misfortune have various contributing factors as their causes. Some illnesses, the so-called karma-induced illnesses, originated from a previous life. They are medically incurable, no matter how much money is spent. These may be attributed to karma. If you have a cold, headache, or fever, it may also be karma related, but not necessarily caused by karma from past lives. Hence, karma is sometimes directly responsible for certain things taking place, but other times may not be so directly involved. The point is, in all matters, Buddhism has always opposed taking the dualistic approach, affirming one thing while negating the other. The same applies to karma.

[Excerpt from Luminous Wisdom Book Series ~ The Right View : On Cause and Effect]