Lomustine Side Effects: What to Expect and When to Call Your Doctor

Lomustine (Gleostine) is a powerful chemotherapy drug with a well-characterized side effect profile. Understanding what side effects to expect — and which ones require urgent medical attention — is critical for patients receiving this medication. This guide covers everything you need to know about lomustine side effects in plain language.

The Most Important Warning: Delayed Myelosuppression

Lomustine has an FDA boxed warning — the most serious safety warning the FDA issues — for delayed, cumulative, and potentially fatal bone marrow suppression (myelosuppression).

What makes this particularly tricky is the timing: Unlike many chemotherapy drugs where side effects peak within a week, lomustine's myelosuppression is delayed by 28 to 42 days after your dose. Many patients feel relatively well in the first few weeks, then experience a dangerous drop in blood counts in weeks 4–6.

This delayed suppression also accumulates over cycles — each dose adds to the bone marrow suppression from prior doses. Your oncologist will monitor your blood counts weekly for at least 6 weeks after every lomustine dose.

Common Side Effects of Lomustine

These side effects are expected in many patients but are generally manageable:

Nausea and vomiting — Usually occur within 3–6 hours of taking your dose and typically resolve within 24 hours. Taking lomustine on an empty stomach at bedtime can help reduce nausea. Anti-nausea medications prescribed by your oncologist will also help.

Loss of appetite — May last several days after the dose

Hair loss (alopecia) — Hair loss may occur with lomustine treatment; typically reversible after treatment ends

Mouth sores (oral ulcers) — Can be reduced with good oral hygiene; your oncologist may recommend oral rinses

Diarrhea — Usually mild; stay hydrated and contact your care team if severe

Fatigue — Expected during chemotherapy; balance rest with gentle activity as tolerated

Serious Side Effects — When to Call Your Doctor Urgently

Call your oncologist immediately or go to the emergency room if you experience any of the following:

Fever (100.4°F / 38°C or higher) — In a patient with low white blood cells, fever can be the only sign of a serious infection that can become life-threatening within hours

Unusual bruising or bleeding — Signs of dangerously low platelet counts (thrombocytopenia); includes nosebleeds, gum bleeding, unusual skin bruising

Shortness of breath or persistent cough — May indicate pulmonary toxicity (lung damage), which can develop as early as 6 months into treatment and is more common with cumulative doses above 1,100 mg/m²

Decreased urination, swelling in legs/ankles — May signal kidney problems; progressive renal failure has been reported with lomustine

Yellowing of the eyes or skin (jaundice) — May indicate liver toxicity

Neurological changes — New or worsening confusion, weakness, or vision changes should always be reported to your oncology team

Long-Term and Delayed Risks

Secondary cancers: Lomustine may increase the risk of developing other cancers, including leukemia, months to years after treatment

Fertility effects: Lomustine may reduce fertility in both men and women; discuss fertility preservation options with your oncologist before starting treatment if you hope to have children

Pregnancy risk: Lomustine can cause serious fetal harm. Women must use effective contraception during treatment and for 2 weeks after the last dose; men must use contraception for 3.5 months after the last dose

Safe Handling at Home

Always wear disposable gloves when handling lomustine capsules

Never break, crush, or open capsules

If the medication contacts skin, wash immediately with soap and water

Keep out of reach of children — lomustine is extremely toxic in overdose

Pregnant women should avoid handling lomustine entirely

If you're struggling to find lomustine at a pharmacy, medfinder can help. Also see our guide to lomustine drug interactions to know what medications and substances to avoid while on treatment.