glp1-oral-contraceptive-interaction

name

glp1-oral-contraceptive-interaction

description

Counsel patients on oral hormonal contraceptive interaction with tirzepatide (Mounjaro) — requirement for non-oral contraception or added barrier method for 4 weeks after initiation and 4 weeks after each dose escalation. Use when a clinician asks "does Mounjaro affect the pill", "tirzepatide and oral contraceptive", "contraception counselling on GLP-1", or when a woman of childbearing potential is starting or escalating Mounjaro. Grounded in the Mounjaro Canadian Product Monograph (April 2026) — drug-drug interaction with combined oral contraceptives.

Tirzepatide (Mounjaro) — Oral Contraceptive Interaction

Purpose

Tirzepatide meaningfully reduces oral contraceptive absorption via delayed gastric emptying. This requires a specific, time-limited contraception strategy — not a blanket warning. Get it wrong and an unintended pregnancy results on a drug that is contraindicated in pregnancy.

Activation

Trigger when:

• Woman of childbearing potential is starting tirzepatide.
• Patient on tirzepatide is undergoing a dose escalation.
• Contraception review in a patient on Mounjaro.
• Questions about any GLP-1 RA and the pill (note: the monograph-documented effect is for tirzepatide specifically; class effect not formally quantified but plausible).

The PK Effect (why it matters)

Single 5 mg tirzepatide dose co-administered with combined OCP (ethinyl estradiol 35 µg + norgestimate 0.25 mg):

• C_max reduced 55–66%
• AUC reduced 16–23%
• t_max delayed 2.5–4.5 h

Mechanism: delayed gastric emptying, greatest after the first dose and after each escalation — diminishes on steady state at a given dose.

The Rule

For women using oral hormonal contraceptives on Mounjaro:

Switch to a non-oral method (IUD, implant, injection, patch, ring)

OR

Add a barrier method (condom) for:

• 4 weeks after initiation of Mounjaro, AND
• 4 weeks after EVERY dose escalation

Practical Counselling Script

"Mounjaro slows stomach emptying, which means the pill can be absorbed much less — up to about two-thirds less after a dose increase. For 4 weeks after we start the medication, and for 4 weeks after every time we step up your dose, you'll need to use a condom as well as your pill, OR switch to a method that doesn't go through the stomach — IUD, implant, injection, patch, or ring."

Dose-Escalation Timing Example

A patient starting Mounjaro 2.5 mg, escalating every 4 weeks:

Week	Dose	Barrier/non-oral needed?
0–4	2.5 mg (start)	YES (post-initiation window)
4–8	5 mg	YES (post-escalation window)
8–12	7.5 mg	YES
12–16	10 mg	YES
16–20	12.5 mg	YES
20–24	15 mg (max)	YES
24+	15 mg steady	No further escalation; risk diminished but barrier still reasonable until next visit confirms tolerance

In practice: a patient undergoing the full 5-step escalation is covered by the rule for the entire ~6-month titration period.

Pregnancy Context

• Mounjaro is contraindicated in pregnancy.
• Long half-life (~5 days) → discontinue ≥ 1 month before planned pregnancy.
• Animal reproductive toxicity demonstrated.
• Contraceptive failure on tirzepatide is a preventable harm — this is why the rule is strict.

What This Skill Does NOT Cover

• Semaglutide (Wegovy/Ozempic/Rybelsus): monograph does not specify an OCP barrier rule. Counsel on pregnancy-avoidance generally; use clinical judgement.
• Liraglutide, dulaglutide: no specific OCP rule.
• Only tirzepatide carries the 4-week escalation barrier rule in its Canadian label.

Rules & Constraints

1. Non-oral beats barrier — if feasible, switch to IUD/implant/injection/patch/ring rather than rely on condom compliance.
2. Every escalation resets the 4-week clock — not just the first one.
3. Document the counselling in the record.
4. Rybelsus (oral semaglutide) is a different concern — 30-min dose separation for any oral co-medication; see glp1-gi-ae-pharmacological-rescue.
5. Emergency contraception: if sexual exposure during the at-risk window, offer per standard pathway; Cu-IUD is preferred on a drug that delays gastric emptying.

Reference

MOUNJARO Product Monograph, Eli Lilly Canada, 2026-04-02. §9.4 Drug-Drug Interactions (Oral Contraceptives), §7 Reproductive Health.