Headache is a common side effect with Bactrim (sulfamethoxazole / trimethoprim) and may occur in up to 10% of patients. Low blood sugar, low sodium blood levels and rarely, aseptic meningitis are other side effects of Bactrim that may lead to a headache.
You or a caregiver should immediately contact your doctor or call 911 right away if you experience serious side effects with Bactrim, such as:
- a persistent or rapidly worsening headache
- a stiff neck
- seizures (convulsions)
- trouble with your eyesight
- a slow or abnormal heartbeat
- problems moving your arms or legs
- loss of balance
- confusion or memory loss.
Review other Bactrim side effects below, that may also be associated with a headache and may require immediate medical attention.
The most common side effects you are likely to experience with Bactrim are nausea, vomiting, a skin rash or itching. Dehydration and eating a poor diet (due to nausea) can also lead to a headache. If you are vomiting or are not eating adequately or drinking enough fluids, discuss this with your healthcare provider right away.
What is Bactrim?
Bactrim (and Bactrim DS) are prescription oral antibiotics that combine two antibiotics in one tablet: sulfamethoxazole and trimethoprim.
Bactrim is used to treat a wide variety of bacterial infections, such as lung, urinary tract , ear, and intestine. It may also be used to treat 'travelers' diarrhea. It does not treat a viral infection like the flu or COVID.
- Bactrim belongs to a drug class called sulfonamides and folate-antagonists. It is usually taken as an oral tablet and a liquid suspension by mouth, but also comes in injection form.
- The "DS" in Bactrim DS stands for double-strength. Other brand names for sulfamethoxazole / trimethoprim include Septra, Septra DS and Sulfatrim Pediatric.
- Sulfamethoxazole and trimethoprim also comes as a generic option, and may be more affordable for you.
Why does Bactrim cause a headache?
A headache is a very nonspecific symptom and can occur for a variety of reasons, some of them serious. In many cases, your headache may not be related to Bactrim, but may be due to the infection and illness you have, poor sleep and may be temporary. Contact your healthcare provider to discuss your headache symptoms and treatment.
There are several other serious side effects related to Bactrim that can lead to a headache, including low blood sugar (hypoglycemia), low sodium in your blood (hyponatremia) and aseptic meningitis.
Low blood sugar (hypoglycemia)
Bactrim can cause low blood sugar (hypoglycemia) in some patients which may lead to a headache. In patients without diabetes, this can occur after a few days of Bactrim therapy. If you have problems with your kidney, liver, are malnourished or are receiving high doses of Bactrim, you may be at greater risk for low blood sugar.
Cases of hypoglycemia are rarely seen in patients treated with Bactrim that do not have diabetes, and usually occurs after a few days of therapy. If you have kidney problems, liver disease, are not well nourished or are receiving high doses of Bactrim, you may be at greater risk of low blood sugar while taking Bactrim.
Contact your doctor or other healthcare provider if you have symptoms of low blood sugar such as:
- dizziness or confusion
- feeling sleepy or a behavior change similar to being drunk; feeling unsteady
- blurred vision
- cold sweats, pale skin that is cool to the touch
- feeling weak, shaky or nervous
- trouble with your thinking or memory
- drowsiness
- increased hunger
- headache
- nausea
- have a fast heartbeat
- trouble breathing
- unusual tiredness.
Low blood sodium (hyponatremia)
Bactrim can also cause low blood sodium (hyponatremia) in certain patients, particularly those being treated for Pneumocystis jirovecii pneumonia, which is a lung infection caused by a fungus.
Most people who get this form of pneumonia have a weakened immune system, like HIV/AIDS, or take medicines that can reduce the body’s ability to fight germs and sickness (like corticosteroids).
Signs of low sodium levels can include side effects like:
- headache
- trouble focusing
- memory problems
- feeling confused
- weakness
- seizures (convulsions)
- change in balance.
Speak to your doctor if you experience these side effects while taking Bactrim.
Aseptic meningitis
A serious, but rare side effect related to Bactrim is aseptic meningitis. Aseptic meningitis is a serious form of non-bacterial meningitis and causes inflammation of the membranes covering the brain and spinal cord. Causes of aseptic meningitis can include certain medicines, fungi, or viruses.
Call your doctor right away if you have symptoms such as:
- a headache
- fever
- chills
- upset stomach or throwing up
- stiff neck
- rash
- trouble looking at bright lights; light sensitivity
- unusual sleepiness
- confusion
Related: Side effects and warnings related to Bactrim (in more detail)
This is not all the information you need to know about Bactrim (sulfamethoxazole / trimethoprim) for safe and effective use and does not take the place of your doctor’s directions. Review the full product information and discuss this information and any questions you have with your doctor or other health care provider.