I would not expect much in the way of results from topical yohimbine. In one relatively recent study that compared the effects of several topical fat burners, everything worked EXCEPT yohimbine:
"All trials except yohimbine ointment gave significantly more girth loss from the treated thigh (p < 0.05 to p < 0.001)" (1)
However another trial did show that yohimbine helped to burn fat (2). Interestingly both trials were conducted by the same researcher. So the scientific basis for the claims that topical yohimbine burns is not strong.
Regarding estrogen and fat, in hamsters estrogen upregulates alpha 2 receptors (3) leading to reduced fat burning, but in humans estrogen downregulates lipoprotein lipase ( the major fat accumulating enzyme ) activity in fat cells and is thought to be a fat burning agent (4), with progesterone being responsible for fat accumulation in women's hips and thighs.
(1) Obes Res 1995 Nov;3 Suppl 4:561S-568S
Topical fat reduction.
Greenway FL, Bray GA, Heber D.
Department of Medicine, UCLA School of Medicine, Torrance, CA, USA.
(2) Clin Ther 1987;9(6):663-9 Related Articles, Links
Regional fat loss from the thigh in obese women after adrenergic modulation.
Greenway FL, Bray GA.
Department of Medicine, UCLA School of Medicine.
(3) Endocrinology 1986 Jun;118(6):2210-6
Estradiol treatment decreases the lipolytic responses of hamster white adipocytes through a reduction in the activity of the adenylate cyclase catalytic subunit.
Pecquery R, Leneveu MC, Giudicelli Y.
(4) Am J Obstet Gynecol 1998 Jan;178(1 Pt 1):101-7
Estrogen regulation of adipose tissue lipoprotein lipase--possible mechanism of body fat distribution.
Price TM, O'Brien SN, Welter BH, George R, Anandjiwala J, Kilgore M.
Department of Obstetrics and Gynecology, Greenville Hospital System, SC 29605, USA.