Saffron is a spice derived from the flower Crocus sativus and has traditionally been used to flavor food. It has gained scientific attention recently for its potential anti-depressant effects and is available in extract form as a dietary supplement.
Enough evidence has accumulated that we can be confident that saffron has notable antidepressant effects, consistently outperforming placebo. Some studies have tested saffron against reference drugs, such as the SSRI fluoxetine and have found the effects to be comparable, though saffron still has less evidence and less of a real-world track record than many drugs. Additionally, it appears to have anti-anxiety effects, though the evidence for this isn't as strong, and more research in specific anxiety disorders is needed. Some preliminary research suggests that it may help to alleviate the symptoms of premenstrual syndrome, menopause, various inflammatory conditions, and improve sleep, but much more research is needed to be confident in its efficacy for these purposes.
It should be noted that the vast majority of studies have been conducted in Iran, which produces much of the world's saffron. While this should not discredit the results of the studies, and most seem to take reasonable measures to reduce the risk of bias, more replication from other researchers would go a long way toward solidifying saffron's effects. Additionally, much of the depression research from other countries is industry-funded, which carries an obvious conflict of interest.
There's also the possibility of a small effect on blood glucose, LDL, inflammation, liver health, blood vessels, and erectile dysfunction, but these are all of speculative efficacy.
Trials generally suggest that the standard dose of 30 mg of extract is largely safe, without meaningful differences in adverse events compared with placebo. Doses of 60 mg of saffron extract and 400 mg of ground powder may increase the risk for hypotension, reduce hemoglobin, increase blood urea, and reduce the concentration of platelets and immune cells, though these effects aren't usually particularly potent. One study found an increase in creatinine in both a 200 mg and 400 mg group, with a greater increase for 200 mg, though another study that used 300 mg didn't find an effect. High doses may also increase the risk of headaches, nausea, sedation, hypomania, abnormal uterine bleeding, and diarrhea.
Saffron might also not be the most cost-effective supplement, and some alternatives could be more desirable, but this valuation will differ considerably between individuals.
Just like with pharmaceutical drugs, chemicals in herbs can interact negatively with each other, and consumers must always be vigilant about their drug/herb combinations and seek professional advice.
There's apparently much more to saffron than crocin, and studies that have found benefits of saffron haven't found as great an effect from an equivalent amount of crocin. There may be some instances where crocin is comparably effective, but more research is needed to determine this.