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<sub>max</sub> reduced 55–66%**
- AUC reduced 16–23%
- t<sub>max</sub> 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.