Black currant has many health benefits.

Cancer protection by black currant
The fruit juice of black currant (Ribes nigrum) contains  proanthocyanidins, anthocyanins and a polysaccharide-rich substance, which is designated cassis polysaccharide (CAPS), with macrophage-stimulating activity. Especially, its interleukin (IL)-1beta-inducing activity is remarkably high, compared with other fruit juice preparations. CAPS was found to consist of rhamnose, mannose, arabinose, galactose, xylose, and glucose. CAPS shows cytotoxicity directly against tumor cells.

Pharmaceutical Biology. 2014. Protective effects of raw and cooked blackcurrant extract on DNA damage induced by hydrogen peroxide in human lymphoblastoid cells.

Fatty acids in black currant seed oil, nutritional value
Black currant seed oil contains 14% alpha-linolenic (18:3n3), 12% gamma-linolenic (18:3n6), 47% linoleic (18:2n6) and 2.7% stearidonic (18:4n3) acids.

Red currant composition
Ribes rubrum has anthocyanins and proanthocyanidins.

Availability
You can find currant jelly, black currant seed oil, red currant jelly, dried currant, black currant tea, and black currant juice.

Black currant seed oil side effects
No major side effects have yet been noted with black currant seed oil. As with any oil, it is best to use in moderation.

Black currant seed oil research
Black currant seed oil and fish oil supplements differ in their effects on fatty acid profiles of plasma lipids, and concentrations of serum total and lipoprotein lipids, plasma glucose and insulin.
J Nutr Biochem. 2005.
Fifteen healthy females participated in a randomized, double-blind, crossover study including two 4-week periods with either 3 g/day of black currant seed oil or 2.8 g/day of fish oil separated by a 4-week washout period. The results show that black currant seed oil supplementation increased the proportion of 18:3n6 in triacylglycerols (TAG) and cholesteryl esters (CE), and that of dihomo-gamma-linolenic (20:3n6) in TAGs, CEs and glycerophospholipids (GPL). Proportion of 18:3n6 was higher after black currant seed oil than after fish oil in TAGs and CEs, and that of 20:3n6 in TAGs, CEs and GPLs. Black currant seed oil supplementation caused only minor changes in the proportions of 20:5n3 or 22:6n3. Serum levels of LDL cholesterol were lower after black currant seed oil compared to fish oil. Plasma glucose concentration decreased during the fish oil supplementation.

Weight loss
Q. Does black currant seed oil lead to weight loss?
     A. I can't see how ingesting black currant seed oil would lead to weight loss.