The Misconception: Unpacking the Discontinuation Rumor
Contrary to a widely held belief, Milk of Magnesia has not been broadly discontinued [1.2.4]. The active ingredient, magnesium hydroxide, remains an approved and available over-the-counter (OTC) treatment for occasional constipation and indigestion [1.5.9, 1.6.3]. The perception of its disappearance stems from several distinct factors rather than a market-wide withdrawal. For instance, while major brands like Phillips' are still in production, certain store-specific brands or flavor variations have been permanently discontinued [1.2.7, 1.3.7]. Additionally, temporary shortages have been caused by recalls. In June 2022, the FDA announced a voluntary recall by Plastikon Healthcare for some lots of its Milk of Magnesia oral suspension due to microbial contamination [1.2.1, 1.4.3]. Such events, though isolated to a specific manufacturer, can create gaps on store shelves and lead consumers to believe the product is gone for good. While one specific Phillips' product was cancelled by Health Canada in 1996, other versions of the brand's products remain for sale in Canada [1.3.1, 1.3.4].
The Pharmacology of Magnesium Hydroxide
Milk of Magnesia's effectiveness lies in its dual-action nature, driven by its simple chemical composition, Mg(OH)₂.
As a Saline Laxative
Its primary use is for the short-term relief of occasional constipation [1.6.2]. Magnesium hydroxide is classified as an osmotic laxative [1.5.4]. It works by drawing water from the surrounding tissues of the body into the intestines. This influx of water has two effects: it softens the stool, and it increases the volume of the stool, which in turn increases pressure within the intestine. This pressure stimulates the intestinal muscles (a process called peristalsis), leading to a bowel movement, typically within 30 minutes to 6 hours of consumption [1.6.2]. This mechanism is generally effective but it's important to drink a full glass of water with each dose to aid the process and prevent dehydration [1.6.3].
As an Antacid
Magnesium hydroxide also functions as a powerful antacid [1.6.1]. The hydroxide ions (OH⁻) react with and neutralize the hydrochloric acid (HCl) in the stomach. This reaction forms magnesium chloride (MgCl₂) and water, thereby raising the stomach's pH and providing relief from heartburn, indigestion, and sour stomach [1.6.1].
Factors Influencing Market Presence
While not discontinued, the landscape for Milk of Magnesia has certainly changed. Several factors contribute to its shifting role in the modern pharmacy aisle.
- Supply Chain Disruptions: The production of raw magnesium has faced global challenges. A significant portion of the world's magnesium supply comes from China, where production has, at times, been curtailed to meet energy and emissions targets [1.4.1]. This can create ripple effects, leading to shortages in various magnesium-based products.
- Rise of Alternatives: Modern pharmacology has introduced a wide array of alternatives for constipation, each with a unique profile. Patients and doctors now have more choices, some of which may be perceived as more convenient or having a better side-effect profile for long-term management.
- Safety and Side Effect Profile: Milk of Magnesia is intended for short-term use only, and guidelines advise against using it for more than a week without consulting a doctor [1.6.2]. The most common side effect is diarrhea [1.6.6]. A more significant risk exists for individuals with kidney disease. Impaired kidneys cannot effectively excrete excess magnesium, which can lead to a toxic buildup known as hypermagnesemia, with symptoms like muscle weakness, confusion, and irregular heartbeat [1.6.3, 1.6.6].
Comparison of Common OTC Laxatives
To understand its place in the market, it's helpful to compare Milk of Magnesia to its main competitors.
| Laxative Type | Example Brand(s) | Mechanism of Action | Onset Time | Common Side Effects |
|---|---|---|---|---|
| Osmotic (Saline) | Phillips' Milk of Magnesia | Draws water into the colon to soften stool and stimulate movement [1.5.8]. | 30 mins - 6 hours [1.6.2] | Diarrhea, cramping, bloating, increased thirst [1.5.8, 1.6.7]. |
| Osmotic (Other) | MiraLAX | The active ingredient, polyethylene glycol 3350, also draws water into the colon [1.5.5]. | 1 - 3 days [1.5.5] | Bloating, gas, cramping; generally considered to have fewer side effects [1.5.5, 1.5.8]. |
| Stimulant | Dulcolax, Senokot | Triggers rhythmic contractions of the intestinal muscles to move stool along [1.5.8]. | 6 - 12 hours (oral) [1.5.5] | Stomach cramping, belching, diarrhea, potential for dependency with long-term use [1.5.8]. |
| Bulk-Forming | Metamucil, Citrucel | Absorbs water to form soft, bulky stool, which naturally stimulates the colon [1.5.8]. | 1 - 3 days [1.5.9] | Bloating, gas, cramping, especially if not taken with enough water [1.5.8]. |
| Stool Softener | Colace (Docusate) | Adds moisture to the stool, making it softer and easier to pass without stimulating the bowels [1.5.8]. | 12 - 72 hours [1.5.5] | Generally mild; less effective than other types for significant constipation [1.5.5]. |
Conclusion: A Market Shift, Not a Disappearance
The question 'Why was milk of magnesia discontinued?' is rooted in valid consumer observations—temporary empty shelves, the disappearance of specific brands, and the prominent marketing of newer alternatives [1.2.7, 1.4.3]. However, the product itself has not been removed from the market. It remains a proven, effective, and fast-acting option for occasional constipation relief [1.2.4]. Its journey reflects the evolution of the pharmaceutical industry, where new innovations and complex global supply chains constantly reshape the choices available to consumers. For those who rely on it, Milk of Magnesia is still available, though it might share more shelf space with competitors than it did in decades past.
For more information on the pharmacology of laxatives, an authoritative source is MedlinePlus, a service of the National Library of Medicine. You can find more here.
