What is Keflex (Cephalexin)?
Keflex, the brand name for the generic drug cephalexin, is a first-generation cephalosporin antibiotic [1.3.4]. It's a widely prescribed medication used to treat a variety of bacterial infections by inhibiting the synthesis of the bacterial cell wall [1.7.1]. Doctors may prescribe Keflex for respiratory tract infections, ear infections, skin infections, bone infections, and urinary tract infections [1.7.4]. It is only effective against bacterial infections and will not work for viral illnesses like the common cold or flu [1.3.4]. The typical adult dosage is 250 mg every 6 hours or 500 mg every 12 hours, though it can be adjusted based on the severity of the infection [1.7.2].
The Link: Does Keflex Cause Anxiety?
Yes, anxiety is a potential side effect of taking Keflex. Patient-reported data shows that anxiety is mentioned as a side effect, with one source noting it in 7.3% of users who reported side effects [1.2.2]. Official drug information lists agitation, restlessness, nervousness, confusion, and anxiousness among the possible neuropsychiatric side effects [1.2.1, 1.3.6, 1.4.2]. While gastrointestinal issues like diarrhea and nausea are the most frequent side effects, central nervous system (CNS) effects can and do occur [1.4.2].
Some individuals have reported feeling "super anxious," having mood swings, and feeling more sad or depressed while taking cephalexin [1.2.2]. These mental and mood changes are considered unlikely but serious side effects that warrant a discussion with a healthcare provider [1.3.3].
The Mechanism: How Can an Antibiotic Affect Mood?
The connection between antibiotics and mental health is an area of growing research, primarily focusing on the gut-brain axis [1.5.2]. Antibiotics, by design, alter the bacterial makeup of the gut (the microbiota). This disruption, known as dysbiosis, can have far-reaching effects [1.6.3]. Gut microbes play a role in brain function by influencing the production of neurotransmitters like serotonin, which is a key mood stabilizer [1.5.2]. A reduction in serotonin is linked to both anxiety and depression [1.5.2].
Additionally, cephalosporin antibiotics can have direct effects on the central nervous system. The ß-lactam ring in their chemical structure is thought to have epileptogenic properties and may cause neurotoxicity by competitively inhibiting gamma-aminobutyric acid (GABA), the primary inhibitory neurotransmitter in the brain [1.8.1]. By interfering with GABA, the neuronal threshold for excitation can be lowered, leading to symptoms like agitation, confusion, and in rare cases, seizures [1.8.1]. Risk factors for neurotoxicity include impaired renal function (since the drug is cleared by the kidneys), older age, and pre-existing CNS conditions [1.8.1, 1.8.5].
Comparing Common and Rare Side Effects of Keflex
It's important to distinguish between the most common side effects and rarer, but potentially more serious, adverse events. Taking Keflex with food may help alleviate some of the common gastrointestinal symptoms [1.2.5].
| Side Effect Category | Common Side Effects | Rare but Serious Side Effects |
|---|---|---|
| Gastrointestinal | Diarrhea, nausea, vomiting, stomach pain, indigestion [1.2.7, 1.4.2] | Severe or bloody diarrhea (Clostridioides difficile-associated diarrhea) [1.4.1, 1.7.1] |
| Neurological/Psychiatric | Dizziness, headache, fatigue [1.2.7] | Anxiety, agitation, confusion, hallucinations, seizures [1.4.2, 1.4.3, 1.4.1] |
| Allergic Reactions | Minor skin rash [1.4.4] | Anaphylaxis, hives, swelling of the face/throat (angioedema), Stevens-Johnson syndrome [1.7.1] |
| Other | Genital or anal itching, vaginal yeast infections [1.2.5, 1.4.1] | Liver or kidney problems, low blood cell counts, joint pain [1.4.1, 1.2.7] |
What to Do If You Experience Anxiety on Keflex
If you experience anxiety or other significant mood changes while taking Keflex, it's crucial to contact your healthcare provider [1.2.1]. They can help determine if the symptom is related to the medication, the underlying infection, or another factor. Do not stop taking the antibiotic without medical advice, as failing to complete the full course can lead to antibiotic resistance and a return of the infection [1.7.4].
Your doctor may suggest:
- Monitoring symptoms: If the anxiety is mild, they may advise you to finish the course while monitoring your symptoms.
- Supportive care: Techniques for managing anxiety, such as mindfulness, deep breathing exercises, and ensuring adequate rest, can be beneficial.
- Dietary support: Consuming fiber-rich foods and probiotics after the antibiotic course may help in restoring a healthy gut microbiome, which can be beneficial for mental well-being [1.6.6].
- Switching medications: In cases of severe or distressing neuropsychiatric symptoms, your doctor might decide to switch you to a different class of antibiotic.
Conclusion
While not the most common side effect, Keflex (cephalexin) can cause anxiety, agitation, and other neuropsychiatric symptoms. This link is likely due to the drug's impact on both the central nervous system and the gut-brain axis. Most side effects are mild and gastrointestinal in nature, but any severe or distressing mental health changes should be reported to a doctor immediately. Understanding the potential for these side effects empowers patients and clinicians to make informed decisions about managing bacterial infections safely and effectively. For more detailed information, one authoritative source is the U.S. Food and Drug Administration (FDA) prescribing information for Keflex [1.7.1].
