Placebo
Not scoundrely enough...
Explanation:
Those who take me, won't know me: placebo is often used in control groups when evaluating new medicine and treatments. Test persons aren't supposed to know its not the real thing. They take sugar pills. Those who know me, won't want me: if you know what placebo is, and that something is placebo, the placebo effect will generally be smaller than otherwise. You're less enthusiastic if you know it's fake. Those who want me, will make me: researchers want the sugar pills, not the patients. Those who make me, will give me away: the point is to fool someone else, not to eat/inject it for yourself.