Ingredients and substances in the plant
Goji berry has polysaccharides, betaine, cerebroside, beta-sitosterol, p-coumaric, various vitamins, and carotenoids such as beta carotene and zeaxanthin. The name goji appears to be an English contraction of the Mandarin name, gouqi (pronounced goo-chee) or Gou Qi Zi.

Health benefit
Goji berry has been used for centuries in Asia for eye health benefit and to maintain vitality. We are not aware of any long term published research regarding the use of a supplement in humans or the benefit of drinking the juice. There are countless claims when one searches online for goji berry, but most of these claims are premature and not based on results of human studies. The plain fact is research in humans is lacking, at least in the Western world.
   Some of the online goji berry health benefit claims include such promises as, "Would you believe the average woman in the Himalayan Hunza tribe lives to be 100? And that arthritis, chronic fatigue syndrome, sexual dysfunction and depression are totally unknown to them? Their secret? The berry of the goji vine. Never heard of it? You're not alone.
   We do believe that it has health benefits and future research will indicate which of the goji marketing claims will turn out to be accurate and which will turn out to be overly enthusiastic. For the time being, it appears that one health benefit that has promise is in the realm of vision health. Goji berry has a high level of zeaxanthin which is a carotenoid, along with lutein, necessary for optimal eyesight. We would suggest, though, rather than consuming goji berry predominantly, it would be a good idea to consume a variety of berries - cranberry, blueberry, strawberry, etc - in order to ingest a number of different phytonutrients.

Antioxidant
Lycium barbarum goji juice improves in vivo antioxidant biomarkers in serum of healthy adults.
Nutr Res. 2009.
Although Lycium barbarum goji and active compounds have a high in vitro antioxidant score as determined by simple chemical reaction methods, their in vivo antioxidant effects in humans have not been extensively examined. After our earlier report that an LBP-standardized Lycium barbarum preparation (GoChi) helps prevent oxidant stress-related conditions in humans, our present study examined the hypothesis that the antioxidant effects of GoChi result from its ability to enhance endogenous antioxidant factors. We investigated the effects of GoChi in a 30-day randomized, double-blind, placebo-controlled clinical study. The study population included 50 Chinese healthy adults aged 55 to 72 years. In vivo antioxidant markers, consisting of serum levels of superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), and lipid peroxidation (indicated by decreased levels of malondialdehyde, MDA) were examined preintervention and postintervention with GoChi or placebo (120 mL/d). Our results indicate that GoChi increased antioxidant efficacies in humans by stimulating endogenous factors and suggest that continued use beyond 30 days might help prevent or reduce free radical-related conditions.

Goji berry study by FreeLife, who have their own branded goji product, shows health benefits
A randomized, double-blind, placebo-controlled, clinical study of the general effects of a standardized Lycium barbarum Juice, GoChi.
J Altern Complement Med. 2008.
This randomized, double-blind, placebo-controlled clinical trial is the first study reported from outside China that has examined the general effects of the orally consumed goji berry, Lycium barbarum, as a standardized juice (GoChi; FreeLife International LLC, Phoenix, AZ) to healthy adults for 14 days. Significant differences between day 1 and day 15 were found in the GoChi group in increased ratings for energy level, athletic performance, quality of sleep, ease of awakening, ability to focus on activities, mental acuity, calmness, and feelings of health, contentment, and happiness. GoChi also significantly reduced fatigue and stress, and improved regularity of gastrointestinal function. In contrast, the placebo group showed only two significant changes (heartburn and happiness). No significant changes in musculoskeletal or cardiovascular complaints were observed in either group. All parametric data (body weight, etc.) were not significantly different between groups or between day 1 and day 15 for either group. Our results clearly indicate that daily consumption of GoChi for 14 days increases subjective feelings of general well-being, and improves neurologic / psychologic performance and gastrointestinal functions. The data strongly suggest that further research is indicated to confirm and extend knowledge of the potential effects of Goji berry upon human health.

Animal studies
Goji berry, when given to animals, has been found to protect heart tissue from chemotherapy drug damage, to protect brain cells from oxidative harm, and to protect the liver from alcohol excess.

Goji berry side effects, safety
As of 2011, no goji berry side effects have been reported in the medical literature. High doses could induce alertness at bedtime and perhaps interfere with optimal sleep. As to goji juice side effects, it is difficult to expect any problems with drinking a couple of ounces a day unless it is mixed with other fruits that you may have an allergic reaction to.

Vision and eyesight
Goji berry is well known for having high nutritional value. Research shows it contains many vitamins, minerals, carotenoids and flavonoids that support vision health. Some of these nutrients include vitamins A, C and E, and carotenoids, beta-carotene, lutein and zeaxanthin. Goji berry is one of nature's richest sources of zeaxanthin. It contains about 100 to 200 mg of zeaxanthin per 100 grams.

Protection of heart tissue from chemotherapy drug toxicity
Protective effect of Lycium barbarum on doxorubicin-induced cardiotoxicity.
Phytother Res. 2007.
In rodents given doxorubicin, a drug used in chemotherapy, goji berry administration reduced the toxicity to heart muscle from the drug. The antitumor activity of doxorubicin was not compromised by goji berry, which allows it to be used together with the drug.