“Why Does Metformin Smell Like Fish? Uncover the Surprising Answer Now!”

Metformin, an oral diabetes medication, typically does not smell like fish. However, in some rare cases, certain brands and batches of metformin might have a fishy odor due to impurities or degradation of the active ingredient in the medication called metformin hydrochloride. This fishy smell can be a result of the compound trimethylamine, which is naturally found in fish and can be produced as a byproduct when metformin breaks down. It is important to note that if you have concerns regarding the smell or the effectiveness of your medication, it is always recommended to consult with a healthcare professional or pharmacist.

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Metformin: Unlocking the Mystery Behind its Peculiar Fishy Odor


For individuals who have been prescribed metformin, it is no secret that this medication can possess a rather peculiar and distinctive odor. Many users liken this scent to that of fish, leaving them perplexed and curious about its origin. In this article, we will delve into the realms of chemistry and medicine to unravel the enigma behind why metformin smells like fish.

The Metabolic Maverick:

Metformin is an oral medication commonly prescribed for managing type 2 diabetes. It is renowned for its ability to effectively reduce blood sugar levels and improve insulin sensitivity. Despite its efficacy, metformin is sometimes associated with a side effect that impacts the olfactory senses, causing it to emanate a fish-like aroma.

1. Chemical Composition:

To comprehend why metformin may have such a distinct odor, it is essential to examine its chemical composition. This medication belongs to the biguanide class of drugs, with its active ingredient being metformin hydrochloride. The molecular formula of metformin is C4H11N5, while its molecular weight rests at 165.63 g/mol. These specific chemical properties lay the foundation for the fishy scent mystery.

2. Volatile Organic Compounds (VOCs):

Metformin contains specific chemical groups known as amines, which are nitrogen-containing compounds. When these amines degrade, they release volatile organic compounds (VOCs) as byproducts. These VOCs contribute to the distinctive aroma associated with the decomposition of metformin, closely resembling the smell of fish.

3. Biological Origins:

The presence of a fishy odor in metformin’s degradation process can be attributed to a peculiar coincidence. Trimethylamine (TMA), one of the VOCs generated by metformin, is also a compound responsible for the distinctive fishy odor found in spoiled fish. TMA is synthesized in the human body through various metabolic processes involving nitrogenous compounds, which eventually undergo chemical transformation into TMA.

4. Metabolism and Excretion:

Metformin is predominantly eliminated from the body unchanged, accounting for its intake-to-output odorous conversion. In humans, metformin is not metabolized by the liver, but rather excreted through the kidneys. During this excretion, the metabolic byproducts combine with water, pH levels, and other factors, which may ultimately influence the peculiar scent associated with the drug.

5. Genetic Variation:

Furthermore, genetic variation amongst individuals may contribute to the perception of the fishy odor more strongly in some users compared to others. Enzymes responsible for converting TMA into odorless molecules are encoded by different genes. Consequently, genetic variations can affect these enzymes’ efficiency, potentially leading to increased detection of the fishy smell when taking metformin.


In-depth exploration of the chemistry and biological processes behind metformin’s fishy odor has shed light on why this medication possesses such a distinctive scent. The presence of volatile organic compounds, particularly trimethylamine, and the interplay of metabolic processes and genetic variation contribute to the intriguing phenomenon. Understanding these factors can help individuals taking metformin feel reassured that this smell is a result of normal drug metabolism. With the knowledge gained from this article, readers can now appreciate the complexities of metformin’s smell, debunking the mystery surrounding its fishy fragrance.

FAQs on why does metformin smell like fish

1. Why does metformin smell like fish?
Metformin may have a fishy smell due to the presence of an impurity called trimethylamine (TMA). This impurity can form during the manufacturing process.

2. Is the fishy smell in metformin harmful?
No, the fishy odor in metformin does not pose any health risks. It is simply a cosmetic issue, and it does not affect the effectiveness of the medication.

3. Can metformin smelling like fish cause side effects?
No, the fishy smell itself does not cause any side effects. The active ingredient in metformin remains the same, regardless of the smell.

4. Can the fishy smell of metformin be reduced or eliminated?
Pharmaceutical companies are continually working to minimize or eliminate the fishy smell in metformin. Different manufacturing processes are being explored to achieve this.

5. How common is the fishy odor in metformin?
The fishy smell in metformin is relatively rare, affecting only a small percentage of users. Most individuals taking metformin do not experience this smell.

6. Does the fishy odor indicate that the metformin is expired?
No, the fishy smell in metformin does not indicate expiration. Metformin tablets are typically stable for a long period, and the smell is unrelated to its shelf life.

7. Can the smell of metformin be masked?
Some patients mix the medication with food or flavored liquids to mask the fishy smell. However, it is essential to check with a healthcare professional before altering the administration of any medication.

8. Does metformin with a fishy smell still work effectively?
Yes, a fishy-smelling metformin tablet is as effective as one without the smell. The active ingredient is not compromised by the odor.

9. Can the fishy odor vary between different brands of metformin?
Yes, the intensity of the fishy smell may slightly differ between different generic brands of metformin. This is due to variations in manufacturing processes and the purity of the active ingredient.

10. Should I be concerned if I experience a fishy smell after starting metformin?
If you notice a fishy smell after starting metformin or if the smell is accompanied by any adverse symptoms, it is crucial to consult your healthcare provider. They can evaluate whether the smell is normal or if further investigation is needed.

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