Lovenox Side Effects: What's Normal and What's Not

If you've been prescribed Lovenox (Enoxaparin), you're probably wondering what side effects to expect. Like all medications, Lovenox can cause side effects — but most are mild and manageable. The key is knowing the difference between a normal reaction and something that needs medical attention right away.

This guide covers the most common side effects, the serious ones to watch for, and practical tips for managing them.

What Is Lovenox?

Lovenox is the brand name for Enoxaparin Sodium, a low molecular weight heparin (LMWH) blood thinner. It's given as an injection under the skin to prevent and treat blood clots. Doctors prescribe it for conditions like deep vein thrombosis (DVT), pulmonary embolism (PE), and clot prevention after surgery or during a heart attack.

For a deeper dive, see our full guide: What Is Lovenox? Uses, Dosage, and What You Need to Know.

Common Side Effects

These are the side effects most people experience. They're usually mild and tend to improve as your body adjusts to the medication.

Injection Site Reactions

This is the most common side effect by far. You may notice:

• Bruising at or near the injection site
• Pain or tenderness where the needle went in
• Small hard lumps under the skin
• Redness or irritation

These reactions are normal and happen because Lovenox is a blood thinner — it makes you bruise more easily. Rotating your injection sites (alternating between the left and right sides of your abdomen) can help reduce irritation.

Mild Bleeding or Bruising

You may notice that you bruise more easily than usual, or that small cuts take longer to stop bleeding. This is expected with any blood thinner. Minor nosebleeds and bleeding gums are also relatively common.

Nausea

Some people feel mildly nauseated, especially when first starting Lovenox. This usually goes away on its own within a few days.

Fever

A low-grade fever can occur, particularly after surgery when Lovenox is used for clot prevention. If your fever is persistent or high (over 101°F / 38.3°C), contact your doctor.

Mild Swelling

Some patients notice mild peripheral edema (swelling in the hands, feet, or ankles). Let your doctor know if it becomes bothersome.

Elevated Liver Enzymes

Blood tests may show temporarily elevated AST and ALT levels. This is usually not something you'd feel — it shows up in lab work. Your doctor will monitor this.

Serious Side Effects — Call Your Doctor Right Away

While uncommon, these side effects require immediate medical attention. Don't wait to see if they go away on their own.

Signs of Major Bleeding

Because Lovenox prevents blood clotting, it can sometimes cause dangerous bleeding. Call your doctor or go to the ER immediately if you experience:

• Blood in your urine (pink, red, or dark brown)
• Blood in your stool (red blood or black, tarry stools)
• Vomiting blood or material that looks like coffee grounds
• Coughing up blood
• Unusual or heavy vaginal bleeding
• Bleeding that won't stop from a cut or wound
• Sudden severe headache, confusion, or vision changes (may indicate brain bleeding)

Heparin-Induced Thrombocytopenia (HIT)

HIT is a rare but serious reaction where the medication triggers your immune system to destroy platelets. Paradoxically, this can cause new blood clots rather than bleeding. Symptoms include:

• New swelling, pain, or warmth in a leg or arm
• Chest pain or difficulty breathing
• Skin changes near the injection site (darkening, blisters, or tissue death)

Your doctor will monitor your platelet count with blood tests, especially during the first few weeks of treatment.

Spinal or Epidural Hematoma

This is the subject of Lovenox's boxed warning — the most serious FDA warning. If you receive a spinal or epidural injection (such as for anesthesia) while on Lovenox, there's a risk of bleeding in the spinal area that can cause permanent paralysis. Symptoms include:

• Back pain
• Numbness or weakness in your legs
• Loss of bladder or bowel control

This is a medical emergency. Tell any doctor who is planning a spinal procedure that you are on Lovenox.

Severe Allergic Reaction

Though rare, some people may have an allergic reaction to Enoxaparin. Seek emergency help if you experience:

• Hives, rash, or itching
• Swelling of the face, lips, tongue, or throat
• Difficulty breathing

Note: Lovenox is derived from pork. If you have a known allergy to pork products, tell your doctor before starting treatment.

Hyperkalemia

Lovenox can sometimes cause elevated potassium levels in the blood. Symptoms may include muscle weakness, irregular heartbeat, or tingling. Your doctor may check potassium levels periodically.

Side Effects in Specific Populations

Pregnant Women

Lovenox is commonly used during pregnancy and is considered safer than warfarin for the developing baby. However, the multi-dose vial contains benzyl alcohol, which should be avoided. Pregnant women should use the preservative-free prefilled syringes. Talk to your OB/GYN about any concerns.

Elderly Patients

Older adults have a higher risk of bleeding with Lovenox, partly because kidney function tends to decline with age. If you're over 75, your doctor may use a lower dose and monitor you more closely.

Patients With Kidney Problems

Lovenox is cleared through the kidneys. If your kidneys aren't working well (creatinine clearance below 30 mL/min), the drug can build up in your body and increase bleeding risk. Your doctor will adjust your dose accordingly.

Underweight Patients

People weighing less than 45 kg (about 99 pounds) may have higher drug exposure and increased bleeding risk. Careful monitoring is important.

How to Manage Side Effects

Here are practical steps to minimize discomfort while taking Lovenox:

For injection site bruising:

• Rotate injection sites — alternate between the left and right sides of your abdomen
• Don't rub the injection site after injecting
• Apply a cold compress (not ice directly) for a few minutes before injecting to numb the area
• Leave the air bubble in the syringe — it helps prevent bruising

For mild bleeding:

• Use a soft toothbrush
• Be careful with sharp objects
• Use an electric razor instead of a blade
• Avoid contact sports or activities with high injury risk

For nausea:

• Eat small, frequent meals
• Avoid lying down immediately after eating
• Stay hydrated

To reduce overall risk:

• Take Lovenox exactly as prescribed — don't skip doses or double up
• Avoid medications that increase bleeding risk unless approved by your doctor, including NSAIDs like Ibuprofen and Naproxen. See our drug interactions guide for a complete list.
• Limit alcohol, which can increase bleeding risk
• Tell all your healthcare providers — including dentists — that you're taking Lovenox

Final Thoughts

Most people tolerate Lovenox well, and side effects are usually limited to minor bruising at the injection site. But because it's a blood thinner, you should always be alert for signs of unusual bleeding. When in doubt, call your doctor.

If you're having trouble finding Lovenox at your pharmacy, use Medfinder to check real-time pharmacy availability — no phone calls required.