What are the Side Effects of One A Day Women's Active Metabolism?

January 7, 2026 •

4 min read

According to a 2018 study, nearly one-third of Americans take a multivitamin, but not all supplements are without side effects, especially those with specialized formulations like One A Day Women's Active Metabolism. While generally considered safe for most users, it is crucial to understand the potential adverse effects and how to take the supplement correctly to minimize risks.

Quick Summary

Potential side effects of One A Day Women's Active Metabolism include mild gastrointestinal issues, temporary changes in stool color due to iron, and, in rare cases, allergic reactions. Overconsumption of specific nutrients, especially iron and fat-soluble vitamins, can pose greater risks and lead to more serious complications.

Key Points

Gastrointestinal Distress: Many users experience temporary constipation, diarrhea, or an upset stomach, often mitigated by taking the vitamin with food.
Iron-Related Issues: The iron content can cause stools to turn black and may lead to constipation or nausea; a sign of iron's presence, not necessarily harm.
Risk of Overdose: Excessive intake, particularly of fat-soluble vitamins (A, D) and minerals like iron, can lead to dangerous levels and serious health problems over time.
Allergic Reactions: Though rare, symptoms like rash, swelling, or difficulty breathing require immediate medical attention and may be caused by active or inactive ingredients.
Ingredient-Specific Effects: The inclusion of chromium and high doses of B-vitamins can cause specific side effects such as headaches or flushing in sensitive individuals.
Mitigating Side Effects: Taking the supplement with a meal and staying hydrated can significantly reduce the occurrence of common side effects.
Important Medical Advice: Individuals with pre-existing conditions, such as liver or stomach issues, should always consult a doctor before starting this or any new supplement.

Understanding One A Day Women's Active Metabolism Side Effects

One A Day Women's Active Metabolism is a multivitamin formulated to support healthy metabolism and provide essential nutrients for women. It contains a blend of vitamins and minerals, including B-vitamins, iron, and chromium, which are intended to help convert food into energy. However, like any supplement, it can cause side effects in some individuals, particularly those with existing health conditions or nutrient sensitivities. For most, these effects are mild and temporary, but understanding them is key to a safe and positive experience.

Common Gastrointestinal Side Effects

The most frequently reported side effects are related to the digestive system. These are typically not cause for alarm and may subside as your body adjusts to the supplement. If you experience these effects, try taking the multivitamin with a meal to improve absorption and minimize stomach upset.

Common side effects include:

Upset Stomach or Nausea: Often one of the first side effects users notice, this can be caused by the body adjusting to the concentration of vitamins and minerals. Taking the pill with food can often prevent this discomfort.
Constipation: Minerals like iron and calcium, both common in multivitamins, can lead to constipation in some people. Increasing fluid intake and dietary fiber can help alleviate this.
Diarrhea: Conversely, some individuals may experience diarrhea, which can also be related to the mineral content, particularly magnesium and iron.
Stool Discoloration: Iron, a key ingredient, is known to cause stools to turn black or dark green. This is a normal and harmless effect of iron supplementation.

Potential Issues with Specific Ingredients

The specific blend of ingredients in the Active Metabolism formula can contribute to particular side effects, especially if you are also getting these nutrients from other dietary sources.

High Iron Content: While vital for women's health, excessive iron intake can lead to serious issues, including stomach pain, vomiting, and, in severe cases, organ damage. Accidental overdose of iron is also a leading cause of fatal poisoning in young children.
Chromium Overload: The Active Metabolism formula contains chromium, which is often included to support metabolism. While typically safe, extremely high doses of chromium can cause side effects like headaches, vertigo, and nausea.
B-Vitamins: Though important for energy, over-supplementation of B-vitamins can lead to minor side effects such as flushing, an unpleasant taste in the mouth, or gastrointestinal discomfort.
Fat-Soluble Vitamins: Excess amounts of fat-soluble vitamins (A, D, E, and K) can accumulate in the body and become toxic. Overdosing on Vitamin A, for instance, can lead to liver toxicity and bone weakening.

Rare and Serious Side Effects

While uncommon, certain serious side effects require immediate medical attention. These are typically associated with an allergic reaction or an overdose.

Allergic Reaction: Symptoms such as a rash, hives, swelling of the face, tongue, or throat, or difficulty breathing warrant immediate medical help. This is rare but possible, especially for those with sensitivities to inactive ingredients like soy, which is found in some brands.
Overdose Symptoms: Severe overdose can present with symptoms including severe stomach pain, nausea and vomiting that do not stop, yellowing of the skin or eyes (jaundice), dark urine, and mental/mood changes. If an overdose is suspected, seek emergency medical care immediately.

Comparison of One A Day Multivitamins


Feature	One A Day Women's Active Metabolism	One A Day Women's Complete	One A Day Women's 50+
Primary Focus	Energy and metabolism support.	General health and immune support.	Tailored for women over 50.
Key Ingredients	B-Vitamins, Chromium, Iron.	Calcium, Vitamin D, Folic Acid.	Higher Vitamin D and B12, less Iron.
Potential Side Effects	Nausea, constipation, diarrhea, stool discoloration.	Similar GI issues, often milder.	May have lower risk of iron-related GI issues.
Consideration	Best for those actively managing metabolism.	Good for basic daily nutritional needs.	Designed for age-specific requirements.
Who Should Be Cautious	Individuals with iron sensitivity or existing metabolic issues.	Anyone with pre-existing liver or stomach problems.	People monitoring calcium or vitamin B12 levels.

Safely Taking One A Day Women's Active Metabolism

To minimize the risk of side effects, it's important to follow the recommended dosage and consider the following tips.

Take with Food: The most effective way to reduce gastrointestinal discomfort is to take the multivitamin with a full meal.
Stay Hydrated: Drinking plenty of water can help alleviate issues like constipation.
Consult a Healthcare Professional: Before starting any new supplement, speak with your doctor or pharmacist, especially if you have pre-existing health issues or are taking other medications. They can help determine if the supplement is right for you and monitor any potential interactions.
Monitor Symptoms: Pay attention to how your body reacts. While mild discomfort is normal, persistent or severe symptoms should be discussed with a doctor.

Conclusion

While One A Day Women's Active Metabolism provides essential nutrients aimed at supporting energy and metabolism, it's not without potential side effects. Mild gastrointestinal issues are common and often temporary, while more serious complications from overdose or allergic reactions are rare but require immediate attention. By understanding the risks, taking the supplement as directed, and consulting a healthcare provider, you can safely navigate its use and decide if it is the right addition to your wellness routine.

For more detailed information, you can explore supplement safety guidelines from authoritative sources like the National Institutes of Health.

Frequently Asked Questions

Yes, nausea is a possible side effect, especially when first starting the multivitamin or taking it on an empty stomach. Taking it with food can help alleviate this discomfort.

The black or dark green color in your stools is a harmless and common side effect caused by the iron content in the multivitamin. It is not a cause for concern unless accompanied by other symptoms.

Yes, although rare, an allergic reaction can occur. Seek immediate medical help if you experience a rash, hives, swelling, or difficulty breathing.

If you suspect an overdose, especially if you experience severe stomach pain, persistent vomiting, or mental/mood changes, seek emergency medical attention or call a poison control center right away.

It is possible. Always inform your doctor or pharmacist about all the products you are using, including prescriptions, over-the-counter drugs, and herbal supplements, to avoid potential interactions.

Pregnant individuals should consult their doctor before using this multivitamin, as some of its ingredients can pose risks in large doses. For example, excess Vitamin A during pregnancy can increase the risk of birth defects.

The supplement is formulated with B-vitamins, chromium, and other nutrients that play a role in metabolism. However, it is not a weight-loss pill, and a balanced diet and exercise are key for a healthy metabolism. The effect is typically a nutritional boost, not a drastic change.