Cycloserine: what it treats and how to use it safely

Cycloserine is an antibiotic used mainly as a second-line drug for drug-resistant tuberculosis (TB). Doctors turn to it when first-line TB medicines don’t work or when bacteria are resistant. It’s not a casual antibiotic; you’ll usually see it in combination with other TB drugs under close medical supervision.

What cycloserine treats and how it's used

For adults with resistant TB, cycloserine is usually given by mouth. Typical dosing is 250–500 mg twice a day (total 500–1,000 mg daily), but exact doses depend on your weight, other medicines, and kidney function. Kids get lower, weight-based doses. If you have kidney disease, your doctor will lower the dose or space doses farther apart because the drug clears more slowly.

It’s not a take-it-alone medicine. Cycloserine is part of a regimen with several other TB drugs. Stopping it early or using it alone risks treatment failure and more resistance.

Side effects, warnings and practical tips

The biggest issue with cycloserine is neuropsychiatric side effects. That includes anxiety, mood changes, confusion, hallucinations, and even seizures at higher doses. You’re more at risk if you have a history of depression, psychosis, epilepsy, or heavy alcohol use. If you notice new mood swings, worsening depression, or any odd thoughts, call your provider right away.

Many doctors add vitamin B6 (pyridoxine) to the treatment. B6 can lower the chance of nerve and mood problems linked to cycloserine. Ask your clinician about the right B6 dose for you — it’s a common and simple preventive step.

Other common side effects are headache, dizziness, and gastrointestinal upset. Because cycloserine can lower the seizure threshold, avoid heavy drinking and be cautious with other medicines that increase seizure risk (for example, bupropion or certain antidepressants). If you’re on anti-seizure medication or have seizures, your doctor will weigh risks and benefits carefully.

Before starting cycloserine, expect basic tests: kidney function, a mental health check, and a full medication review to spot risky interactions. During treatment, your care team will monitor symptoms and labs and adjust dose if needed. If you’re pregnant or planning pregnancy, talk to your doctor — cycloserine is not a routine choice in pregnancy unless the benefits outweigh the risks.

Practical tips: take cycloserine at the same times every day, follow food instructions from your provider (some people tolerate it better with food), and never stop it without medical advice. Keep a short symptom diary — note sleep, mood, headaches, and any muscle twitching — and bring it to appointments. That helps your care team catch problems early.

Cycloserine is a useful drug for tough TB cases, but it needs respect. Good communication with your doctor, simple prevention like pyridoxine, and watching for mental or neurological warning signs make a big difference in staying safe while on this medicine.