How long does magnesium citrate take to work?

In this article:

• How long does magnesium citrate take to work?
• For constipation
• For sleep and relaxation
• Comparing forms of magnesium
• Considerations for use
• The bottom line

In this article

• How long does magnesium citrate take to work?
• For constipation
• For sleep and relaxation
• Comparing forms of magnesium
• Considerations for use
• The bottom line

Magnesium facilitates more than 300 enzyme reactions and biochemical processes in the body, including energy production, nerve and muscle function, bone development, and blood pressure and blood sugar regulation. This important mineral is naturally present in many foods but can also be found as an added ingredient in supplements, fortified foods like cereals, and in medications.

Magnesium citrate is one such medication that contains magnesium. This medication belongs to a class of drugs called osmotic or saline laxatives. Laxatives treat constipation by softening and inducing regular bowel movements. Magnesium citrate is taken in liquid form and can work within 30 minutes or a few hours. It is an organic salt compound formed by combining magnesium with citric acid. Magnesium supplementation generally has been studied for benefits including migraine prevention, bone health, and sleep quality, though the evidence strength varies by condition.

How quickly does magnesium citrate work?

“Magnesium citrate typically works within about 30 minutes to six hours, but the duration can vary from person to person,” says Reshma Kapadia Patel, a Pharm.D. in Dallas, Texas, and the founder of WiseMedRx. 

Magnesium citrate works as a laxative by drawing water into the intestines. This increase in gut water softens stools, induces bowel movements, and generally makes them easier to pass. It is available over the counter for short-term, occasional relief of constipation. Healthcare providers sometimes include magnesium citrate as part of bowel preparation regimens before procedures such as colonoscopy, though polyethylene glycol-based preparations are more commonly used as the primary agent.

Factors like hydration, individual metabolism, dose taken, and how sensitive your digestive system is can all affect how quickly it works. People who are more dehydrated or have slower gut motility may notice a delayed effect. “Because of this variability, I usually advise patients to take it when they’ll be at home and have easy access to a bathroom,” Dr. Patel says.

Magnesium citrate for constipation

When taking magnesium citrate for occasional constipation, you can expect a bowel movement within a few hours. It’s important to follow the instructions on the label and stay well hydrated, as the medication works by pulling water into the intestines.

Magnesium citrate is most commonly sold as a pre-mixed liquid in single-dose bottles (typically 10 fl oz / 296 mL) that can be taken directly or chilled for better palatability. Powdered formulations also exist and must be dissolved in water before use. Your healthcare provider or pharmacist can instruct you on how to prepare this solution, based on your specific health history and symptoms. Alternatively, you can follow the instructions on the product label.

Common effects include loose or watery stools (which is the intended effect) and, sometimes, mild abdominal cramping. Taking more than the recommended dose can cause excessive diarrhea, dehydration, electrolyte imbalances, and bloating.

“I encourage patients to avoid relying on osmotic laxatives long-term without evaluating the underlying cause of constipation,” Dr. Patel says. “Sometimes, we can address contributing factors like medications, hydration, or diet rather than adding another product.” 

Factors influencing speed

Several factors can influence how quickly magnesium citrate works in treating constipation. “These factors include differences in dose, hydration level, digestion speed, if the medication was taken on an empty stomach vs after a meal, and other medications,” says Erika Gray, Pharm.D., Founder & Chief Medical Officer at ToolBox Genomics.

• Hydration level: Being well-hydrated is important when taking magnesium citrate. The medication works by pulling water into the intestines. Taking it while dehydrated can worsen dehydration and may also reduce its effectiveness in softening stool. Drink plenty of water before, during, and after taking it.
• Dose: People who take a higher dose of magnesium citrate may see faster results than those who take a lower dose. But keep in mind that you shouldn’t take a high dose unless your provider specifically prescribes it and provides instructions for taking it.
• Digestion speed: Everyone’s digestive system works at varying speeds. Dr. Gray says people who tend to digest more quickly will likely see the effects of the medication faster.
• When the medication is taken: “If you take magnesium citrate on an empty stomach, you may experience the effects more quickly since there is no food in the digestive system to delay the medication,” Dr. Gray says.
• Other medication interactions: Other medications that can cause constipation can also affect how well magnesium citrate works. “For example, if an individual is on an opioid, that could increase the risk of constipation and slow the onset of magnesium citrate,” explains Dr. Gray.

Magnesium citrate for sleep and relaxation

While magnesium citrate is primarily used for constipation, some people take magnesium supplements generally to support relaxation and sleep. However, citrate may not be the ideal form for these purposes. “In terms of onset of action for magnesium when targeting these more subtle, systemic benefits, the medication is likely to help within a few days or one to two weeks of consistent use,” Dr. Gray says.

Therefore, compared to using magnesium for constipation, the onset of systemic benefits of magnesium is more gradual because the body needs time to adjust.

However, Dr. Gray explains that if an individual is looking for a formulation of magnesium that can better target relaxation, mood support, and sleep promotion, a better alternative would be magnesium glycinate. “This form is more gentle on the stomach, highly absorbed, and less likely to cause a laxative effect.”

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The different forms of magnesium and their absorption rates

Magnesium comes in various salts and forms, generally categorized as organic and inorganic. They all differ in how well they are absorbed and what they’re typically used for.

Different forms of magnesium vary in how well and how quickly the body absorbs them, which affects how they’re best used. 

• Better-absorbed forms (typically used for supplementation when magnesium levels are low, or for specific benefits): citrate, glycinate, lactate, taurate, L-threonate, aspartate, bisglycinate.
• Less-absorbed forms (often used as laxatives or antacids, and generally less expensive): oxide, carbonate, sulfate, chloride.
  

All these types of magnesium also have specific uses for which they are best suited. “The key point for patients is that not all magnesium supplements work the same way; some are better for constipation, while others are used more for general supplementation or relaxation,” Dr. Patel says. Notably, magnesium citrate is considered one of the most effective, widely used, and preferred magnesium compounds due to its high bioavailability, multiple benefits, and low risk of adverse effects.  

Important considerations before taking magnesium citrate

Before taking magnesium citrate, Dr. Gray says these are important factors to consider:

• Reason for taking: Whether for constipation relief, bowel prep before a colonoscopy, mood support, sleep promotion, or other purposes, ensure you are taking it for its intended use. 
• Duration of use: Magnesium citrate is not typically intended for long-term use.
• Dosage: Magnesium is an essential electrolyte and mineral that can affect many other organs in the body. Normal blood (serum) magnesium levels typically range from 1.7–2.2 mg/dL, though a blood test is needed to measure this. Keep in mind that blood magnesium levels don’t always reflect overall body magnesium stores. Talk with your healthcare provider if you’re concerned about a deficiency. Magnesium can affect the heart, kidneys, and GI tract, and can cause imbalances if you have too much or too little in your system.
• Kidney function: People with chronic kidney disease, reduced kidney function, or on dialysis should not take magnesium citrate without first consulting their healthcare provider. Damaged kidneys cannot effectively remove excess magnesium from the body, which can lead to dangerously high blood magnesium levels (hypermagnesemia). This can cause muscle weakness, low blood pressure, irregular heartbeat, and, in severe cases, cardiac arrest.
• Hydration: Make sure to drink adequate water while taking this medication to help it work effectively.
• Age: Older adults may be more sensitive to dehydration and to changes in electrolyte levels. 
• Current medications: According to Dr. Gray, certain medications can interact with magnesium. Some examples include thyroid medications (e.g., levothyroxine), proton pump inhibitors (e.g., omeprazole), Neurontin (gabapentin), bisphosphonates (e.g., alendronate), tetracyclines (e.g., doxycycline, minocycline), and fluoroquinolones (e.g., ciprofloxacin, levofloxacin). This is not a complete list, so always discuss all medications, supplements, and herbal remedies with your provider before starting magnesium to ensure safety. 

Taking magnesium two to four hours apart from other medications is enough to prevent interactions, but check with your pharmacist for specific guidance.

The bottom line

The timeframe for the effects of magnesium citrate can vary from person to person, depending on the intended use and other factors such as dosage, digestion speed, and medication interactions. If you are taking it for constipation, you can expect to see effects within 30 minutes to six hours after intake.

But for other systemic uses, such as sleep, mood improvement, and relaxation, expect the effects to come on more gradually, usually within days or a few weeks of use. If you’re using magnesium citrate for constipation and don’t have a bowel movement within six to twelve hours, or if constipation persists beyond a week despite treatment, contact a healthcare provider. For other uses, such as sleep or relaxation support, if you don’t notice effects after a few weeks of consistent use, consult a healthcare professional.

Magnesium citrate can be effective for short-term relief of constipation. It’s important to use it thoughtfully and not rely on it long-term without understanding what’s causing the issue.