Last updated: October 2026
How long magnesium takes to work depends on why you take it. Magnesium citrate can ease constipation within hours. In studies, muscle soreness improved within 10 days, low mood within two weeks, restless legs in four to six weeks, and sleep over about eight weeks. Most people should take it daily for at least two to four weeks before judging.
Below is a timeline by goal and by type of magnesium, the signs it’s working, and how to help it work sooner.
Magnesium timeline at a glance
| Goal | When people notice a difference | Evidence |
|---|---|---|
| Constipation | A few hours (citrate, oxide) | Well established; it’s how magnesium laxatives work |
| Muscle soreness after exercise | Around 10 days | Controlled trial, 350mg a day |
| Low mood | Within 2 weeks | Open-label trial, 248mg a day |
| Restless legs | 4 to 6 weeks | Small study of 10 people |
| Sleep | Up to 8 weeks | Controlled trial in older adults, 500mg a day |
| Tiredness from low intake | 2 to 4 weeks or more | Depends on how low your levels were |
| Stress (low-magnesium adults) | Measured at 4 and 8 weeks | Controlled trial, 264 adults, with or without vitamin B6 |
| Premenstrual mood symptoms | After 1 month | Small trial, 200mg magnesium plus 50mg vitamin B6 |
| Migraine frequency | Weeks 9 to 12 of a 12-week trial | Controlled trial, 600mg a day (above the NHS 400mg guide) |
| Blood pressure | About 1 to 3 months | Meta-analysis of 34 trials; small average changes |
Everyone is different. If your diet is already rich in magnesium, you may notice little change at all.
How long for magnesium to work for sleep?
Some people feel more relaxed on the first evening, but the research points to weeks rather than days. In a controlled trial of 46 older adults with insomnia, those taking 500mg of magnesium a day for 8 weeks fell asleep faster, slept more efficiently and had better insomnia scores than those on placebo. Note that 500mg is above the NHS guide of 400mg a day from supplements.
Give it at least two to four weeks of nightly use. Glycinate is the usual choice for evenings because it’s gentle on the stomach. Read more in magnesium for sleep and the best time to take magnesium.
For anxiety and low mood
A 2017 review of 18 studies found evidence suggesting magnesium may help with feelings of anxiety in people who are prone to it, though the quality of the studies was low. In an open-label trial of adults with mild to moderate depression, 248mg of magnesium a day improved mood scores over six weeks, with effects seen within two weeks. Magnesium contributes to normal psychological function and the normal functioning of the nervous system.
If you’re struggling with your mood, speak to your GP; magnesium isn’t a replacement for treatment. See magnesium for anxiety.
For cramps, soreness and restless legs
- Muscle soreness: in a controlled trial, 350mg of magnesium a day for 10 days reduced muscle soreness and improved how recovered people felt after hard exercise.
- Restless legs: a small study of 10 people found improvements in restless legs and sleep after four to six weeks.
- Night cramps: reviews have found magnesium is unlikely to help typical night cramps in older adults, though some people find it useful.
Magnesium contributes to normal muscle function. See magnesium for cramps and magnesium for restless legs.
For constipation and bloating
This is the fastest effect. Magnesium citrate and oxide draw water into the bowel and often work within a few hours, which is also why too much causes loose stools. Start low. If constipation lasts more than a few weeks, or you notice blood or weight loss, see your GP. See magnesium for constipation and magnesium for bloating.
For tiredness and low levels
If your intake has been low, it can take several weeks of daily supplements to top up your body’s stores. Most of your magnesium is held in your bones and cells rather than your blood, so a standard blood test doesn’t always reflect what’s stored. Magnesium contributes to the reduction of tiredness and fatigue. See signs of magnesium deficiency and how long magnesium stays in your body.
For stress, PMS, migraines and blood pressure
People also take magnesium for other reasons. Here is what the trials measured and how long they ran.
- Stress: in a controlled trial of 264 healthy adults with low blood magnesium, stress scores fell by over 40% after 8 weeks of magnesium, with or without vitamin B6. In the most stressed people, magnesium with B6 did a little better than magnesium alone.
- Premenstrual symptoms: a small trial found 200mg of magnesium plus 50mg of vitamin B6 a day for one month reduced anxiety-related premenstrual symptoms such as nervous tension and mood swings. The effect was small. See PMS symptoms.
- Migraines: in a 12-week controlled trial, 600mg of magnesium a day cut migraine attacks by about 42% in weeks 9 to 12, compared with 16% on placebo. That dose is above the NHS guide of 400mg a day from supplements, and nearly 1 in 5 people had diarrhoea, so speak to your GP before trying it. See magnesium for migraines.
- Blood pressure: a meta-analysis of 34 trials found a median of 368mg a day for about 3 months lowered blood pressure by around 2mm Hg on average. That’s a small change, so never stop prescribed blood pressure medicine.
What happens after you take a dose?
Understanding this helps explain why some effects take weeks.
- First few hours: magnesium is absorbed through the gut. Forms that dissolve well, such as citrate and glycinate, are generally absorbed better than oxide.
- Same day: your kidneys keep blood levels in a narrow range and remove any extra in urine, so healthy people rarely build up too much from food.
- Weeks: most of your magnesium is stored in your bones and muscles. Topping up these stores after a period of low intake is gradual, which is why daily use over weeks matters more than any single dose.
Read more in how long magnesium stays in your body.
How long different types of magnesium take
| Type | Typical use | Timeframe |
|---|---|---|
| Citrate | Constipation, everyday top-up | Hours for constipation; weeks for general use |
| Glycinate | Evenings, stress, sensitive stomachs | Some feel calmer within days; give it 2 to 4 weeks |
| L-threonate | Focus and memory | Studies ran for 3 to 12 weeks |
| Oxide | Cheap tablets, constipation | Hours for constipation; poorly absorbed otherwise |
| Sprays and bath flakes | Relaxation, massage | The bath or massage itself is felt quickly; how much passes through the skin is debated |
Compare forms in magnesium glycinate vs citrate vs threonate and types of magnesium.
Taking magnesium with other supplements
| Combination | What the research shows | Timeframe studied |
|---|---|---|
| Magnesium and vitamin B6 | Similar to magnesium alone for stress overall; slightly better in people with severe stress. Also tested for premenstrual mood symptoms | 1 month (PMS) to 8 weeks (stress) |
| Magnesium and L-theanine | No combined trials. L-theanine on its own (200mg a day) improved sleep and stress scores in a small trial | 4 weeks (L-theanine) |
| Magnesium and vitamin D | Magnesium is needed to activate vitamin D in the body, so low magnesium may affect how well vitamin D works | Not a timed effect |
| Magnesium and ashwagandha | No combined trials. Ashwagandha trials usually ran 6 to 8 weeks | See ashwagandha vs magnesium |
| Magnesium and melatonin | Melatonin is prescription-only in the UK. See melatonin in the UK | Ask your GP |
Our Magnesium Glycinate Sleep Complex combines magnesium bisglycinate and citrate with L-theanine in a berry evening drink. Magnesium contributes to normal psychological function and to the reduction of tiredness and fatigue.
How much magnesium should you take? (UK)
| Amount | Source | |
|---|---|---|
| Daily need, men (19 to 64) | 300mg | NHS |
| Daily need, women (19 to 64) | 270mg | NHS |
| From supplements | 400mg a day or less is unlikely to cause harm | NHS (Department of Health and Social Care) |
| Too much, short term | Over 400mg can cause diarrhoea | NHS |
The NHS says most people can get all the magnesium they need from a varied diet, including spinach, nuts and wholemeal bread. See foods high in magnesium and magnesium side effects.
Signs magnesium is working
- You find it easier to wind down in the evening
- Fewer muscle twitches or cramps
- Less tiredness through the day
- More regular bowel movements
- You feel generally calmer
Keep a simple note of your sleep and symptoms for a few weeks so you can see real changes.
Why isn’t my magnesium working?
- Not long enough. Most effects in trials took 2 to 8 weeks of daily use.
- The wrong form for your goal. Oxide is cheap but poorly absorbed; citrate suits constipation; glycinate suits evenings. See types of magnesium.
- Missed days. Taking it every day matters more than the exact time.
- Magnesium wasn’t the cause. Poor sleep, tiredness and low mood have many causes, from stress to low iron or thyroid problems. See why am I always tired? and underactive thyroid symptoms.
- Lots of alcohol or caffeine, which disturb sleep and increase magnesium loss.
- A medicine that lowers magnesium. The MHRA has warned that long-term use of proton pump inhibitors (such as omeprazole), especially for over a year, can cause low magnesium. Some diuretics can too. Speak to your GP or pharmacist.
How to help magnesium work sooner
- Choose a well-absorbed form, such as glycinate or citrate, rather than oxide.
- Take it every day at the same time.
- Take it with food if it upsets your stomach.
- Split larger amounts into two doses.
- Eat magnesium-rich foods too: leafy greens, nuts, seeds, wholegrains and beans.
- Cut back on alcohol, which increases how much magnesium you lose.
- Check medicine timing. Take some antibiotics and osteoporosis medicines a few hours apart from magnesium, and ask your pharmacist.
The NHS says adults need 300mg a day (men) or 270mg (women), and 400mg a day or less from supplements is unlikely to cause harm. Our Magnesium Glycinate Sleep Complex provides 148mg of magnesium per serving from bisglycinate and citrate, as a warm evening drink.
FAQs
How long does it take for magnesium to work?
It depends on your goal: hours for constipation, around 10 days for muscle soreness, two weeks for mood in one study, and up to eight weeks for sleep. Give it at least two to four weeks.
How long does magnesium glycinate take to work for sleep?
Some people feel calmer within a few days, but studies of magnesium and sleep ran for around eight weeks. Take it nightly for at least two to four weeks before judging.
Can you feel magnesium working straight away?
Usually only for constipation, where citrate or oxide can work within hours. Other effects build gradually with daily use.
How long does magnesium take to work for anxiety?
Studies suggest a few weeks. In one trial, mood improved within two weeks. Speak to your GP if anxiety is affecting your daily life.
How long does it take to fix low magnesium?
Often several weeks of daily supplements and a magnesium-rich diet. A blood test doesn’t always reflect your stores, so talk to your GP if you think you’re deficient.
Why isn’t my magnesium working?
Common reasons are a poorly absorbed form such as oxide, a low dose, taking it irregularly, not giving it long enough, or that magnesium wasn’t the cause of the problem.
Is it better to take magnesium in the morning or at night?
Either works; consistency matters most. Many people take glycinate in the evening as part of a wind-down routine.
How long does magnesium take to work for migraines?
In a 12-week trial, migraine attacks fell most in weeks 9 to 12 on 600mg a day, a dose above the NHS 400mg guide. Speak to your GP before trying it.
How long does magnesium take to lower blood pressure?
Trials ran for around 1 to 3 months and found small average reductions of about 2mm Hg. Never stop prescribed blood pressure medicine.
Can I take magnesium with L-theanine?
There are no trials of the two together, but they are commonly combined in evening drinks. L-theanine on its own was studied for 4 weeks in a small sleep and stress trial.
Can I take magnesium with vitamin B6?
Yes, they are often combined. In trials, magnesium with B6 was studied for 1 month for premenstrual symptoms and 8 weeks for stress.
Sources
- NHS. Vitamins and minerals: magnesium.
- Abbasi B et al (2012). The effect of magnesium supplementation on primary insomnia in elderly. Journal of Research in Medical Sciences.
- Boyle NB et al (2017). The effects of magnesium supplementation on subjective anxiety and stress: a systematic review. Nutrients.
- Tarleton EK et al (2017). Role of magnesium supplementation in the treatment of depression: a randomized clinical trial. PLoS One.
- Reno AM et al (2022). Effects of magnesium supplementation on muscle soreness and performance. Journal of Strength and Conditioning Research.
- Garrison SR et al (2020). Magnesium for skeletal muscle cramps. Cochrane Database of Systematic Reviews.
- Hornyak M et al (1998). Magnesium therapy for periodic leg movements-related insomnia and restless legs syndrome: an open pilot study. Sleep.
- Pouteau E et al (2018). Superiority of magnesium and vitamin B6 over magnesium alone on severe stress in healthy adults with low magnesemia. PLoS One.
- De Souza MC et al (2000). A synergistic effect of a daily supplement for 1 month of 200mg magnesium plus 50mg vitamin B6 for the relief of anxiety-related premenstrual symptoms. Journal of Women’s Health.
- Peikert A et al (1996). Prophylaxis of migraine with oral magnesium: a prospective, multi-center, placebo-controlled and double-blind randomized study. Cephalalgia.
- Zhang X et al (2016). Effects of magnesium supplementation on blood pressure: a meta-analysis of randomized double-blind placebo-controlled trials. Hypertension.
- Hidese S et al (2019). Effects of L-theanine administration on stress-related symptoms and cognitive functions in healthy adults. Nutrients.
- Uwitonze AM, Razzaque MS (2018). Role of magnesium in vitamin D activation and function. Journal of the American Osteopathic Association.
- de Baaij JHF et al (2015). Magnesium in man: implications for health and disease. Physiological Reviews.
- MHRA (2012). Proton pump inhibitors in long-term use: reports of hypomagnesaemia. Drug Safety Update.
This guide is general information, not medical advice. Evopure makes the Magnesium Glycinate Sleep Complex.
