What Medication Causes Weak Legs? An Overview of Drug-Induced Myopathy

October 12, 2025 •

4 min read

According to studies, drug-induced myopathy is a recognized cause of muscle disease that can range from mild aches to severe weakness. Knowing what medication causes weak legs is crucial for both patients and healthcare providers to manage and mitigate symptoms.

Quick Summary

Many medications can cause muscle weakness, a condition known as drug-induced myopathy. Common culprits include statins, corticosteroids, and diuretics, which affect muscles through various mechanisms. Risk factors can increase susceptibility, and symptoms often improve after discontinuing or adjusting the offending drug. Emergency signs like dark urine require immediate medical attention.

Key Points

Statins are a frequent cause of leg weakness: These cholesterol-lowering drugs can cause muscle pain and weakness through mitochondrial dysfunction, with rare cases progressing to more severe autoimmune myopathy.
Long-term steroid use leads to muscle atrophy: Corticosteroids like prednisone cause muscle weakness and wasting by increasing protein breakdown and decreasing protein synthesis, especially with higher doses.
Diuretics can cause weakness via hypokalemia: Certain diuretics can deplete the body's potassium, which is critical for muscle function, leading to cramps and leg weakness.
Some antibiotics can worsen muscle conditions: Classes such as fluoroquinolones and macrolides can interfere with neuromuscular transmission, posing risks, particularly for individuals with myasthenia gravis.
Chemotherapy can induce nerve damage: Chemotherapy-induced peripheral neuropathy (CIPN) can cause numbness and muscle weakness in the extremities, including the legs.
Prompt medical consultation is crucial: Never stop medication without consulting a doctor; persistent or sudden, severe muscle weakness warrants medical evaluation to rule out rhabdomyolysis or other serious conditions.

Understanding Drug-Induced Muscle Weakness

Drug-induced myopathy is a recognized adverse effect that manifests as muscle pain (myalgia), weakness, or even severe muscle breakdown (rhabdomyolysis). While many factors can contribute to muscle weakness, a comprehensive review of a person's medication regimen is essential to identify the root cause. This condition is often reversible, with symptoms typically improving or resolving after discontinuing or modifying the dosage of the implicated drug. The mechanisms vary widely, from direct toxicity to muscle cells to disrupting essential metabolic functions or causing electrolyte imbalances.

Common Medications That Cause Weak Legs

Statins

Statins are a class of cholesterol-lowering drugs, such as atorvastatin (Lipitor) and simvastatin (Zocor), that are widely prescribed. They are also one of the most commonly reported drugs linked to muscle pain and weakness, with myopathy occurring in a significant percentage of users. The mechanism is not fully understood but may involve mitochondrial dysfunction, which impairs the energy production of muscle cells, and inhibition of the Akt/mTOR pathway, leading to muscle protein degradation. In very rare cases, statins can cause statin-associated autoimmune myopathy (SAAM), which is a rare, severe form of muscle damage that may require immunosuppressive therapy.

Corticosteroids

Corticosteroids, such as prednisone, are potent anti-inflammatory drugs used to treat a variety of conditions. Prolonged use, especially at high doses, can lead to steroid-induced myopathy, characterized by muscle atrophy and weakness, primarily affecting the legs and arms. This occurs through both anti-anabolic mechanisms, which inhibit muscle protein synthesis, and catabolic mechanisms, which increase protein breakdown. In addition, some corticosteroids can cause electrolyte imbalances, further contributing to weakness.

Diuretics

Diuretics, or 'water pills', are often used to treat high blood pressure and fluid retention. Some types, including loop and thiazide diuretics (e.g., furosemide, hydrochlorothiazide), can cause low blood potassium levels, a condition known as hypokalemia. Since potassium is vital for proper muscle function, a deficiency can lead to muscle weakness, fatigue, and cramps. A blood test can help diagnose this, and supplementation or a change in medication may be required.

Certain Antibiotics

While most antibiotics are generally safe, some classes are known to interfere with neuromuscular transmission, potentially worsening or unmasking muscle weakness in vulnerable individuals, particularly those with myasthenia gravis.

Fluoroquinolones (e.g., ciprofloxacin, levofloxacin) carry a black box warning due to their link with exacerbating muscle weakness in myasthenia gravis patients and potentially damaging tendons.
Macrolides (e.g., azithromycin, erythromycin) have also been reported to trigger myasthenia gravis exacerbations.
Aminoglycosides are known to block neuromuscular transmission and are to be used with caution.

Chemotherapy Agents

Chemotherapy-induced peripheral neuropathy (CIPN) is a common side effect of many cancer treatments, particularly with taxanes and platinum-based drugs. This condition involves nerve damage in the extremities, which can lead to muscle weakness, numbness, tingling, and balance problems, particularly affecting the legs and feet in a 'sock-and-glove' pattern. The severity can vary, and while symptoms may improve after treatment, some weakness can persist long-term.

Other Medications

Colchicine: Used for gout, this medication can induce a vacuolar myopathy that typically resolves after discontinuation.
Antimalarials (e.g., hydroxychloroquine): These can cause muscle weakness and pain, which usually resolve once the medication is stopped.
HIV Medications (e.g., zidovudine): Older antiretroviral drugs can affect mitochondria within muscle cells, impairing energy production and causing myopathy.
Opioids: Chronic opioid use can cause myoclonus (involuntary muscle jerking), and withdrawal can lead to uncontrollable leg movements.

Comparison of Medications Causing Leg Weakness


Medication Class	Mechanism(s)	Typical Severity	Common Management
Statins	Impaired mitochondrial function, protein degradation, autoimmune response.	Mild to severe, including rare rhabdomyolysis.	Dose reduction, switching to a different statin, or discontinuation.
Corticosteroids	Increased protein breakdown, decreased synthesis, electrolyte imbalance.	Variable; can be severe with long-term, high-dose use.	Dose reduction or withdrawal; physical therapy.
Diuretics	Electrolyte imbalance, specifically hypokalemia (low potassium).	Mild to moderate; resolves with correction of potassium levels.	Potassium supplementation, switching to a potassium-sparing diuretic.
Fluoroquinolone Antibiotics	Disruption of neuromuscular transmission, tendon damage.	Potentially severe, especially in myasthenia gravis patients.	Discontinuation of the medication.
Chemotherapy Agents	Peripheral nerve damage (CIPN).	Variable; can cause persistent weakness after treatment ends.	Symptom management, physical therapy, dose adjustment.

When to Seek Medical Attention

It is vital to consult a healthcare professional if you experience new or worsening muscle weakness while taking any medication. For drug-induced myopathy, the diagnosis often relies on a process of exclusion, ruling out other conditions. A doctor may check your creatine phosphokinase (CK) levels, which indicate muscle damage. If a medication is suspected, they may recommend a dose adjustment or a change to an alternative therapy.

Seek emergency medical attention immediately if you experience any of the following symptoms:

Sudden or severe weakness, especially on one side of the body.
Severe muscle pain and weakness accompanied by dark-colored urine, which can signal rhabdomyolysis, a medical emergency that can lead to kidney failure.
Weakness that spreads from your legs to your trunk and arms, or difficulty breathing.

Conclusion

While many medications can cause weak legs, it is essential not to stop or alter your treatment plan without medical supervision. The risk of an underlying condition exacerbating could be greater than the medication's side effects. Awareness of the potential for drug-induced myopathy empowers patients to have informed discussions with their healthcare providers. By carefully monitoring for symptoms, discussing potential risks, and seeking timely evaluation, muscle weakness related to medication can often be effectively managed. For detailed information on specific drugs, consult reputable medical databases or speak directly with your doctor.

GoodRx provides details on specific medications that cause muscle weakness.

Frequently Asked Questions

The risk of muscle problems can be dependent on the specific type and dosage of the statin. Some studies suggest that fluvastatin XL and lower doses of rosuvastatin may have lower rates of myopathy compared to others, but individual reactions can vary significantly.

Yes, some antibiotics, particularly fluoroquinolones and macrolides, have been associated with muscle weakness. This is especially relevant for people with pre-existing conditions like myasthenia gravis, where these drugs can worsen symptoms by affecting nerve-muscle communication.

Diuretics can cause muscle weakness by lowering blood potassium levels (hypokalemia). Potassium is an essential electrolyte for muscle contractions, and a deficiency can lead to weakness, cramps, and other symptoms.

Rhabdomyolysis is a severe and potentially life-threatening condition involving the rapid breakdown of muscle tissue. It can be triggered by certain medications, like statins, and manifests with severe muscle pain, weakness, and dark-colored urine. It requires immediate medical attention to prevent kidney damage.

Yes, chemotherapy-induced peripheral neuropathy (CIPN) can damage peripheral nerves and cause long-term muscle weakness in the legs and feet, along with numbness and balance issues.

You should not stop your medication suddenly. Speak to your doctor, who may adjust the dosage, switch you to an alternative drug, or recommend physical therapy. In some cases, the symptoms will subside once your body adjusts to the medication.

Yes, low potassium caused by diuretics can be managed. Your doctor might prescribe potassium supplements, or switch you to a potassium-sparing diuretic. Eating potassium-rich foods like bananas can also help, but often isn't enough on its own.