When Should I Worry About Leg Cramps? How to Tell If It’s Harmless or a Blood Clot

Leg pain and cramping are common and often result from muscle spasms. While this pain can feel severe, it’s usually not serious. But sometimes what feels like a leg cramp may actually be something more serious: a blood clot in your leg, also called deep vein thrombosis (DVT). 

Here, we’ll review both conditions, provide some clues to help tell the difference, and discuss what to do next.

What are leg cramps?

A leg cramp — sometimes called a “charley horse” — is a painful muscle spasm. It happens when a leg muscle suddenly tightens, usually for a brief period (a few seconds to minutes). This most commonly happens in your calf muscle. But it can also happen in the muscles of your thighs or feet.

Causes of leg cramps

Leg cramps can have many different causes, including:

• Tired muscles

• Nerve damage due to neuropathy or trauma

• Electrolyte abnormalities, like low potassium or magnesium levels

• Kidney disease, which often affects electrolyte levels

• Dehydration

• Pregnancy 

• Medications like diuretics for blood pressure, statins for cholesterol, and long-acting beta agonists (LABAs) for asthma

While there are many causes of leg cramps, most of the time it’s not clear why they happen, and they often go away on their own. But in some cases, a leg cramp can be caused by a blood clot.

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Signs that your leg pain may be serious

A leg cramp can be a sign of DVT, which happens when your blood clots inside a vein.

DVTs more commonly occur in the smaller veins that travel deep within your lower legs. But they can also occur in other veins throughout your body. The most common symptoms include:

• Swelling: This may be visible just in your foot or below your knee, or it can affect your whole leg.

• Pain: People often describe a constant, dull pain in your calf, knee, or thigh.

• Redness of the skin: The redness is usually faint and spread out.

• Warmth: The skin over the affected area may feel warmer than the rest of your skin. 

Many times, these symptoms only occur in one leg. But sometimes a DVT (or multiple DVTs) can cause symptoms in both legs. Many other conditions, like cellulitis or lymphedema, can also cause these same symptoms. So, DVT can’t be diagnosed by symptoms alone. 

Usually, an ultrasound is needed for diagnosis. It’s also important to note that DVT doesn’t always cause noticeable symptoms, and many people may not know they have one. In fact, up to 40% of people with DVTs may have no symptoms.

Quiz: Do I have DVT?

How to tell the difference between leg cramps and a clot (DVT)

Leg cramps and DVTs can feel similar. But there are some differences that can help tell them apart:

• Timing: DVT symptoms are usually subtle at first and then gradually increase over days. Cramps, on the other hand, typically start suddenly, feel severe, and last only seconds to minutes before going away. Cramps also most commonly occur in the middle of the night.

• Swelling: New, one-sided leg swelling is more worrisome for DVT. Leg cramps can result from conditions that cause swelling (like kidney disease), but this swelling is typically there all the time

• Warmth and redness: DVTs can cause noticeable redness and warmth in your leg, but this is much less common with cramps.

When to seek care if you are worried about a leg cramp

No one expects you to make this diagnosis on your own. A healthcare professional may order blood tests or do an ultrasound of your veins if they think you may have a DVT. If you have leg pain that is worrying you, reach out to a healthcare professional for help, especially if: 

• Your symptoms feel severe or are significantly impacting your daily activities 

• You have new swelling, redness, or warmth in your leg that wasn’t there before

• You have risk factors for DVTs or blood clots

You have an increased risk of developing a DVT for many different reasons:

• Immobilization: Anything that decreases the amount you use your legs can increase your risk of blood clots. This includes recent surgery, hospitalization, bedrest, or even prolonged travel, like a long flight or road trip. 

• Medical conditions: Certain conditions can make your blood more likely to clot. Some examples are inherited blood disorders, autoimmune diseases, and cancer.

• Pregnancy: If you’re pregnant or recently gave birth, you’re at higher risk because increased estrogen levels affect the way that our blood clots. 

• Medications: Some types of birth control, like the combined oral contraceptive pill, may increase your risk of blood clots — but only by a small amount. Your risk goes up if you also have other risk factors for blood clots. Hormonal replacement therapy pills can also increase your risk of blood clots — but estrogen injections, creams, patches, and gels don’t. 

Seeking help is important because DVTs can lead to a more serious condition called pulmonary embolism (PE). This happens when parts of the clot break off and travel to your lungs. It can cause symptoms like: 

• Shortness of breath

• Chest pain

• Fainting 

PE is a potentially life-threatening condition because it affects your oxygen levels and, in some cases, your blood pressure. If you’re experiencing any of these symptoms, it’s best to see a healthcare professional right away or go to an emergency room to get them checked.

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Written by:

Nicole Andonian, MD

Nicole Andonian, MD, is a private practice anesthesiologist in Orange County, California. Her focus is in general anesthesia, regional anesthesia, and acute pain management.

Edited by:

Karla Robinson, MD

Karla Robinson, MD, is a medical editor for GoodRx. She is a licensed, board-certified family physician with almost 20 years of experience in health through varied clinical, administrative, and educational roles.

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