Are homeopathic medicines effective for weight reduction?

No: Truly homeopathic "medications" are made by repeated dilutions, so that the ingredient is not really in the medication anymore (just the "essence" of it remains). That means there is no active ingredient left to cause any benefit. However, that also implies that the homeopathic "medicine" should be pretty harmless, unless some other non-homeopathic ingredients were added.

Homeopathy & weight: There is no specific homeopathy remedy for weight reduction, because remedies are directed more to internal imbalance in the patient who's suffering symptoms rather than the pathologic condition s/he has. Still, i've seen patients treated homeopathically who became much healthier -- and in that process changed lifestyle enough to lose weight. Prescribed correctly, these medicines are powerful.