Drug facts

Drug interactions

Reviewed August 2026

Insulin and sulfonylureas¹

Section 7.1 states that the product lowers blood glucose, and that when initiating it, prescribers should consider reducing the dose of concomitantly administered insulin or insulin secretagogues such as sulfonylureas, to reduce the risk of hypoglycemia.

How much the hypoglycemia risk moved²

Section 5.7 puts numbers on it. In a trial of patients with type 2 diabetes and BMI of 27 kg/m² or above (Study 2), hypoglycemia — plasma glucose below 54 mg/dL — was reported in 4.2% of treated patients against 1.3% on placebo. Within that trial, patients also taking an insulin secretagogue had a higher rate (10.3%) than treated patients not taking a sulfonylurea (2.1%). The section adds that hypoglycemia has also been associated with the product and with GLP-1 receptor agonists in adults without type 2 diabetes.

Section 5.7 also instructs that patients be informed of the risk and educated on the signs and symptoms, and that blood glucose be monitored in patients with diabetes before and during treatment. Hypoglycemia is one of several warnings that sit alongside the boxed warning about thyroid C-cell tumors.

Oral medicines generally³

Section 7.2 states that the product delays gastric emptying and thereby has the potential to impact the absorption of concomitantly administered oral medications, and that caution should be exercised when oral medications are given alongside it. It singles out two groups for monitoring: oral medications dependent on threshold concentrations for efficacy, and those with a narrow therapeutic index — the example the label gives is warfarin.

Oral contraceptives³

The same section carries specific advice: patients using oral hormonal contraceptives should switch to a non-oral contraceptive method, or add a barrier method, for 4 weeks after initiation and for 4 weeks after each dose escalation. Hormonal contraceptives that are not administered orally should not be affected.

Note the shape of that instruction. It is not once at the start — it recurs at every step up the schedule, which means the number of times it applies depends on how many escalations there are in the approved dosing schedule and its four-week steps.

The measurements behind the warning⁴

Two studies are reported. Following a first dose of 5 mg, acetaminophen maximum concentration was reduced by 55% and its median peak occurred one hour later; after co-administration at week 6 with 15 mg, there was no meaningful impact on acetaminophen peak concentration or timing, and overall exposure over 24 hours was not influenced. With a combined oral contraceptive (0.035 mg ethinyl estradiol and 0.25 mg norgestimate) given alongside a single 5 mg dose, mean peak concentrations of ethinyl estradiol, norgestimate and norelgestromin fell by 59%, 66% and 55%, while mean overall exposure fell by 20%, 21% and 23%, with a delay to peak of 2.5 to 4.5 hours.

The same section notes that in vitro studies showed low potential for tirzepatide to inhibit or induce CYP enzymes or to inhibit drug transporters. In other words the interaction the label is describing is not a metabolic one — it is about the speed at which the stomach empties.

Why the effect fades⁵

Section 12.2 states that tirzepatide delays gastric emptying, that the delay is largest after the first dose, and that this effect diminishes over time. That is why the contraceptive advice attaches to initiation and to each escalation rather than to treatment as a whole, and it is also part of why gastrointestinal symptoms are heaviest early — which is the pattern visible in the side effects reported in 5% or more of trial participants. The mechanism itself is covered in how tirzepatide acts on GIP and GLP-1 receptors.

None of this was studied on a compounded vial⁴

A compounded preparation carries no approved prescribing information of its own, so none of these findings arrive attached to it. That does not make the concerns disappear — it means the document that would normally tell a pharmacist and a patient about them is missing, and the burden falls on the prescriber who has your full medicine list.

Pregnancy and the contraception window are set out separately: what sections 8.1 and 7.2 say →