And they show that smoking can alter the available effective drug action as you said, which is interesting. Many things can alter how a particular drug will affect you. These articles don't, however, claim unilaterally that it applies to all drugs or that the exact amount of loss of efficacy, if any, will be half. (In fact the first article you cite says that sometimes smoking can increase effectivity.)I agree that it would be worth bringing these articles to the attention of your doctor if you're changing your smoking habits.