High-risk medication · Last reviewed: March 2026
ISOTRETINOIN IS A POTENT TERATOGEN (Category X). It must never be used during pregnancy. Any pregnancy occurring during or shortly after treatment carries an extremely high risk of severe fetal abnormalities.
Females of childbearing potential must be enrolled in the appropriate Pregnancy Prevention Programme (iPLEDGE in the USA; local PPP in the UK/EU/Australia) before starting treatment and must comply with all contraception requirements.
This calculator is for educational reference only. All dosing decisions must be made by the treating dermatologist in compliance with local regulations.
Isotretinoin (Accutane, Roaccutane) is an oral retinoid used in the treatment of severe, treatment-resistant acne. Unlike most dermatological therapies, isotretinoin is unique in that its clinical outcome is closely linked to the cumulative total dose received over the course of treatment, rather than just the daily dose. The method is the same weight-based dosing used across other medicines.
A cumulative target of 120–150 mg/kg is associated with the lowest relapse rates (Rademaker, PubMed). Courses falling short of this target — particularly those below 100 mg/kg — carry a significantly higher rate of acne relapse and may require re-treatment.
The daily dose typically ranges from 0.5 mg/kg/day (the common starting point to allow assessment of tolerability) to 1.0 mg/kg/day (the standard maintenance dose). The total course length depends on how quickly the cumulative target is reached at the chosen daily dose.
Enter the patient's weight, age, and sex. Select whether to input the daily dose as mg/kg/day (recommended) or as a fixed mg/day amount. The calculator computes the daily dose in mg, then determines how many effective treatment days are required to reach the selected cumulative target. New to these units? See mg/kg/day vs mg/kg per dose.
Missed days can be entered separately. The calculator subtracts these from the total days elapsed to give an effective treatment days count, allowing accurate tracking of cumulative exposure when doses are missed or held for adverse effects.
The result includes: daily dose, cumulative dose to date (in both total mg and mg/kg), remaining mg/kg to target, and estimated remaining treatment time in days, weeks, and months.
A tablet count estimate is provided based on the selected tablet strength (10, 20, 40, 80, or 120 mg), giving the prescriber a practical supply calculation for the next prescription.
Persistent warnings are displayed for female and non-binary patients (teratogen/PPP reminder), for daily doses exceeding 1.5 mg/kg/day (outside standard range), and for cumulative doses approaching or exceeding 200 mg/kg (unusual high exposure).
The cumulative isotretinoin dose is tracked using three sequential calculations:
The 120 mg/kg cumulative target is the most widely cited threshold for predicting long-term remission. Studies show that patients reaching this target have significantly lower 5-year relapse rates compared to those treated with shorter or lower-dose courses.
A 2025 cohort of nearly 20,000 patients confirmed that higher cumulative totals lower relapse, with no added benefit beyond about 220 mg/kg (JAMA Dermatology, 2025). The 2025 EuroGuiDerm guideline goes further, noting that a single evidence-based target cannot yet be fixed — so clinicians treat to clinical clearance plus a month or two, rather than a number alone (EuroGuiDerm, 2025).
A target of 150 mg/kg is sometimes used in patients with severe, nodular, or scarring acne, or in cases with a history of relapse after a previous course. Higher targets must be balanced against the risk of cumulative toxicity, particularly to the skin, lips, and musculoskeletal system.
Courses below 100 mg/kg are associated with relapse rates of up to 60% within 2 years and are generally considered inadequate for definitive treatment unless limited by side effects or regulatory requirements.
Some prescribers use low-dose, long-duration regimens (e.g., 0.25–0.3 mg/kg/day for 12–24 months), which can achieve the cumulative target with a significantly better tolerability profile — particularly for patients with sebaceous gland sensitivity who cannot tolerate standard doses.
Baseline and monthly blood tests are required for all patients on isotretinoin: full blood count, liver function tests, fasting lipids (triglycerides and cholesterol), and a pregnancy test for all female patients of childbearing potential.
iPLEDGE (USA) and the Pregnancy Prevention Programme (UK/EU) impose strict requirements: two negative pregnancy tests before starting, monthly pregnancy tests during treatment, and compliance with dual contraception throughout treatment and for at least one month after the last dose.
Psychiatric monitoring is required throughout treatment. Isotretinoin has been associated with depression and suicidal ideation in post-marketing surveillance, though causality remains debated. Clinicians should enquire about mood at every visit. More recent population-level evidence is reassuring: a 2024 meta-analysis of over 1.6 million patients found no overall increase in depression or suicide risk among isotretinoin users (JAMA Dermatology, 2024), so individual vigilance — not alarm — is the right posture.
Common side effects include dry skin, cheilitis (dry and cracked lips), dry eyes, nosebleeds, and transient hair thinning — all dose-dependent and reversible on stopping. Triglyceride elevation and transaminase rises are the most clinically significant laboratory abnormalities.
Estimated Course Duration to Reach 120 mg/kg Target: Estimated treatment days at two common daily dose rates to reach a 120 mg/kg cumulative target. Assumes no missed doses. Round daily dose to nearest available tablet strength.
At a 150 mg/kg target, the same daily rates take about 300 days at 0.5 mg/kg/day or 150 days at 1.0 mg/kg/day, regardless of weight.
| Weight (kg) | 0.5 mg/kg/day (mg) | Days at 0.5 mg/kg/day | 1.0 mg/kg/day (mg) | Days at 1.0 mg/kg/day |
|---|---|---|---|---|
| 40 kg | 20 mg | 240 days | 40 mg | 120 days |
| 45 kg | 22 mg | 245 days | 45 mg | 120 days |
| 50 kg | 25 mg | 240 days | 50 mg | 120 days |
| 55 kg | 27 mg | 244 days | 55 mg | 120 days |
| 60 kg | 30 mg | 240 days | 60 mg | 120 days |
| 65 kg | 32 mg | 244 days | 65 mg | 120 days |
| 70 kg | 35 mg | 240 days | 70 mg | 120 days |
| 75 kg | 37 mg | 243 days | 75 mg | 120 days |
| 80 kg | 40 mg | 240 days | 80 mg | 120 days |
| 90 kg | 45 mg | 240 days | 90 mg | 120 days |
| 100 kg | 50 mg | 240 days | 100 mg | 120 days |
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Usman Shaoukat is the founder and editor of BestMedCal. He is a computer and web specialist who researches every BestMedCal tool from published standards and medication-safety references, including NIST, the U.S. FDA, NCBI and the American Academy of Pediatrics. His focus is dose-to-volume calculations and unit conversions. Every formula and worked example is checked against the sources listed on each page. BestMedCal has no clinicians on staff: our tools check arithmetic and explain methods; they do not recommend doses. If you spot an error, contact us and we will review it.