Somewhere around day 26 the craving starts, and by day one you'd trade a kidney for a bar. The usual explanation is that your body "knows" it needs magnesium. Nice story. Here's what has actually been measured, where dark chocolate for period cramps stands up, and where it doesn't.
What magnesium has to do with cramps
Period cramps are the uterine muscle contracting under the push of prostaglandins. Magnesium sits on the other side of that: it's involved in muscle relaxation and, in one early study, in prostaglandin production itself. In a 1989 double-blind trial, 50 women with primary dysmenorrhea took magnesium or placebo for six months. Twenty-one of the 25 on magnesium reported fewer symptoms, and the prostaglandin F2-alpha in their menstrual blood fell to 45% of its starting level, against 90% on placebo.
A 1990 trial in Zurich gave 32 women three doses of 5 mmol magnesium a day (about 365 mg in total) on the day before their period and the first two days. It did little on day one, but eased back and lower-belly pain on days two and three, and the magnesium group missed less work. Only 21 women finished, a number to keep in mind for everything here.
A Cochrane review looked at three such trials and called magnesium "a promising treatment" for period pain while admitting nobody knows what dose or schedule works. ACOG says the same thing more bluntly: magnesium may be helpful, but there isn't enough research to recommend it as a treatment.
Magnesium for period cramps: how much, when, from what
How much. The NIH puts the daily requirement at 310 mg for women 19 to 30, 320 mg for 31 to 50, and 360 mg for girls 14 to 18. The trials above used roughly 360 mg a day on top of food. The NIH also sets a ceiling of 350 mg a day from supplements specifically (food doesn't count toward it), because past that point magnesium's best-known side effect is diarrhea. So: eat freely, supplement carefully.
When. The cramp trials dosed from the day before bleeding through day two or three. The mood study below dosed from mid-cycle. If you only try one window, start the day before you expect your period.
From what. Pumpkin seeds (156 mg an ounce), chia seeds (111 mg an ounce), almonds (80 mg an ounce), cooked spinach (78 mg per half cup), black beans (60 mg per half cup), and dark chocolate, which is where this gets relevant.
How much magnesium is in dark chocolate, really
USDA's database lists 70 to 85% dark chocolate at 228 mg of magnesium per 100 g. A normal serving, 35 g or about a third of a standard bar, is around 80 mg. That's a quarter of your day, not the whole trial dose, and it comes with roughly 200 calories. Milk chocolate is a different food, with far less cacao and far more sugar; read the percentage on the label.
Has anyone tested dark chocolate for period cramps?
A few small groups have. The most careful one is a 2023 randomized trial of 45 midwifery students in Indonesia. On the first day of their period they got either 35 g of 70% dark chocolate, 330 ml of coconut water, or 400 mg of ibuprofen, taken within 15 minutes. Two hours later, pain on a 0 to 10 scale had dropped 3.9 points with the chocolate, 4.6 with ibuprofen and 2.9 with coconut water. The gap between chocolate and ibuprofen was not statistically significant; the gap between both and coconut water was.
Now the limits, because they matter. Nobody was blinded (you know when you're eating chocolate). It was one dose, one day, 15 people per group. And 80 mg of magnesium can't be the whole story two hours later; cocoa flavanols, the sugar, the plain comfort of it, and expectation are all inside that number. We read it as evidence that dark chocolate is worth trying, not as proof of a mechanism.
The mood part is better studied than the pain part
If your period is more mood than cramp, there's a cleaner trial. In 1991, 32 women with PMS took 360 mg of magnesium three times a day from day 15 until their period started, double-blind against placebo. Magnesium significantly improved the "negative affect" cluster, the irritability and low mood, and the total symptom score. It's the study we point to when someone asks about sugar cravings before a period, because the craving and the mood dip usually arrive together.
What we'd actually do
Eat magnesium-rich food all month; that's the base. From the day before your period through day three, add a 35 g piece of 70%+ dark chocolate in the afternoon, and stack it with the things that have stronger evidence: heat on your belly, and ibuprofen at the first twinge if you can take it. Our list of foods that ease period cramps has the rest of the plate.
One thing that did not work for us: a magnesium supplement taken only once the pain had started. Both cramp trials dosed from the day before, and when we waited for day one we got the loose stomach and none of the relief.
This is why we make what we make. Girl Chocolate is a dark chocolate bar built for the days around your period, sold as a pouch of 8 bars so one pouch covers one cycle, with magnesium and other functional ingredients in a bar you'd want to eat anyway. It supports PMS relief* and it's made for your cycle. We'd rather you got magnesium from spinach and seeds too; the bar is the part that fits in a pocket. See the bar.
Print our free period cramp relief cheat sheet: the heat, ginger, magnesium and timing facts from this guide, all on one page. 1 page, PDF, no email needed.
Download the PDFSources
- Seifert 1989, magnesium in primary dysmenorrhea (PubMed)
- Fontana-Klaiber 1990, magnesium in dysmenorrhea (PubMed)
- Proctor 2001, herbal and dietary therapies for dysmenorrhoea (Cochrane)
- NIH Office of Dietary Supplements, Magnesium fact sheet
- Nuha 2023, dark chocolate vs ibuprofen for primary dysmenorrhea (PubMed)
- Facchinetti 1991, oral magnesium and premenstrual mood (Obstet Gynecol)
When to talk to a doctor
Chocolate and magnesium are for ordinary cramps and ordinary moods. See a doctor if you have any of these:
- Pain that stops you doing daily life, even with painkillers
- Bleeding through a pad or tampon every hour
- Pain that suddenly got much worse, or changed its pattern
- Pain with a fever
* These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.
