Women on the combined pill had less than half the lamotrigine in their blood for the same dose
Mean steady-state lamotrigine was 13 micromol per litre in 22 women on combination oral contraceptives against 28 in 30 women not taking them (p < 0.0001), "indicating that LTG plasma levels are reduced by >50% during OC co-medication."
Weak or heavily disputed. Treat as a question, not an answer. how we score evidence
Caveat on this rating: Fifty two women, cross-sectional, levels not outcomes. The size of the effect is consistent with the label, which was written after studies of this kind.
This is the measurement behind the contraceptive warning on the lamotrigine label.
Significant findings
Sabers and colleagues (Neurology, 2003) compared plasma lamotrigine in women taking the drug with and without a combination oral contraceptive. "The mean steady-state plasma concentration of lamotrigine (LTG) was 13 micro mol/L in 22 women taking LTG in combination oral contraceptives (OC) compared with 28 micro mol/L among 30 women on LTG who did not take OC (p < 0.0001)."
Adjusted for dose and weight: "The LTG dose/body weight/plasma concentration was 2.1 L/kg/day in women on OC compared with 0.8 L/kg/day in women without OC (p < 0.0001), indicating that LTG plasma levels are reduced by >50% during OC co-medication."
The authors' recommendation: "It is advisable to monitor LTG plasma levels in conjunction with initiation or withdrawal of OC in women on LTG therapy."
Worth asking
A halving of the level means a dose that controlled mood or seizures before the pill may not after it, and a dose that was right on the pill may be too high after stopping it. This was a small study of women with epilepsy, and it measured levels, not relapses. The question it puts to a prescriber is a simple one: has a lamotrigine level been checked since the contraceptive changed?
Source
Oral contraceptives reduce lamotrigine plasma levels — Sabers A, Ohman I, Christensen J, Tomson T (2003)
Reputable peer-reviewed journal
Read the source: https://doi.org/10.1212/01.wnl.0000076485.09353.7a
DOI: 10.1212/01.wnl.0000076485.09353.7a
How this was scored
- Study design
- Cross-sectional study / survey
- Funding
- Funding not disclosed
- Published in
- Reputable peer-reviewed journal
- Sample size
- 52
- Preregistered
- not recorded
- Conflicts disclosed
- not recorded
- Independent of proponent
- not recorded
- Retracted
- No
Read the full scoring rubric, including what it can't tell you.
Published September 21, 2026.
Questions
How strong is the evidence behind this?
veisund rates this source "contested". Weak or heavily disputed. Treat as a question, not an answer. It scores 39 out of 100 on our published rubric. One caveat travels with that badge: Fifty two women, cross-sectional, levels not outcomes. The size of the effect is consistent with the label, which was written after studies of this kind. The score is calculated from recorded facts about the source — study design, funding, publication venue, sample size, preregistration — not typed in by an editor.
What is the source for this?
Oral contraceptives reduce lamotrigine plasma levels — Sabers A, Ohman I, Christensen J, Tomson T (2003). Published in: Reputable peer-reviewed journal. DOI: 10.1212/01.wnl.0000076485.09353.7a. The full source is linked on this page so you can read it yourself.
Who paid for this research, and does that matter?
Study design: Cross-sectional study / survey. Funding: Funding not disclosed. Independence from the proponent is not recorded. Industry sponsorship is one of the most reliably measured biases in medicine, which is why funding carries real weight in the score rather than sitting in a footnote.
Is this medical advice?
This is information to bring to your prescriber, not medical advice and not a reason to change anything on your own. Nothing here is an instruction to stop or reduce a medication. If you are in crisis, call or text 988.
This is information to bring to your prescriber, not medical advice and not a reason to change anything on your own. Nothing here is an instruction to stop or reduce a medication. If you are in crisis, call or text 988.