Famotidine Before Vyvanse: Safety and Dosing
Taking famotidine before Vyvanse (lisdexamfetamine) is safe without dose adjustment, as famotidine does not interfere with amphetamine pharmacokinetics or metabolism. 1
No Pharmacokinetic Interaction
Famotidine has no clinically significant drug interactions with medications metabolized through hepatic pathways, as it does not interfere with cytochrome P450 enzymes or other metabolic systems 2, 3
The American College of Cardiology specifically notes that H2 blockers like famotidine do not interfere with other drug mechanisms, unlike some PPIs that inhibit CYP2C19 4, 1
Research demonstrates famotidine does not impair drug clearance when co-administered with other medications, showing no kinetic interactions in clinical practice 5
Timing Considerations
Famotidine reaches peak plasma concentrations in 1-3 hours after oral administration, with antisecretory activity beginning within 1 hour 2
Vyvanse demonstrates efficacy starting at 1.5 hours postdose and maintains effect through 13 hours in school-aged children with ADHD 6
Taking famotidine first allows it to establish gastric acid suppression before Vyvanse administration, which is pharmacologically appropriate since Vyvanse absorption is not pH-dependent 2, 6
Standard Dosing Remains Unchanged
Famotidine standard dosing is 20-40 mg daily depending on indication, with oral administration providing 10-12 hours of antisecretory activity 1, 2
No dose adjustment is needed for either medication when taken together, as they work through completely independent mechanisms 4, 1
Clinical Caveats
Famotidine is eliminated primarily through the kidneys (approximately 70%), so dose reduction may be necessary in patients with renal impairment, but this is unrelated to Vyvanse co-administration 2
Tolerance to H2-receptor antagonist therapy develops within 6 weeks of continuous use, requiring periodic reassessment of famotidine efficacy 1
The most common adverse events with Vyvanse include decreased appetite, insomnia, headache, and irritability, which are unaffected by famotidine co-administration 6