Does Acyclovir Interact With Tizanidine?
7.2 Moderate or Weak CYP1A2 Inhibitors Concomitant use of tizanidine with moderate or weak CYP1A2 inhibitors (e.g., zileuton, antiarrhythmics [amiodarone, mexiletine, propafenone, and verapamil], cimetidine, famotidine, oral contraceptives, acyclovir, and ticlopidine) should be avoided.
Severity: Major
Severity basis: drug interactions section (keywords: avoid). Combining Acyclovir (Antiviral (nucleoside analogue)) and Tizanidine (Skeletal muscle relaxant) is classified as a major interaction.
What to Do
The label advises avoiding this combination or using it only under close medical supervision. Talk to your prescriber or pharmacist before combining them.
How This Interaction Works
Interactions like this one can happen when two medicines have overlapping effects, or when one changes how the other is absorbed, broken down, or cleared from the body. Acyclovir is a antiviral (nucleoside analogue) and Tizanidine is a skeletal muscle relaxant; together they are documented as a major interaction. How much this matters depends on your dose, your other medications, and your overall health.
If You Take Both Medications
If you have been prescribed both Acyclovir and Tizanidine, do not start, stop, or change either medication on your own — some medicines are unsafe to stop suddenly. Tell your prescriber and pharmacist that you take both so they can decide whether the combination is right for you, adjust the dose, monitor you more closely, or suggest an alternative.
From the FDA Label
7.2 Moderate or Weak CYP1A2 Inhibitors Concomitant use of tizanidine with moderate or weak CYP1A2 inhibitors (e.g., zileuton, antiarrhythmics [amiodarone, mexiletine, propafenone, and verapamil], cimetidine, famotidine, oral contraceptives, acyclovir, and ticlopidine) should be avoided.
Source: FDA structured product labeling (set_id 01c0d3d3-2373-a1b7-822a-80a66291a248).
Check these against your full medication list in our free Interaction Checker
Frequently Asked Questions
Can you take Acyclovir and Tizanidine together?
Acyclovir and Tizanidine have a documented major interaction. The label advises avoiding this combination or using it only under close medical supervision. Talk to your prescriber or pharmacist before combining them.
How serious is the Acyclovir and Tizanidine interaction?
It is classified as a major interaction, based on the FDA label's drug interactions section (keywords: avoid). A major interaction can cause serious harm and often calls for a change in therapy or close monitoring.
What should I do if I'm taking both Acyclovir and Tizanidine?
If you have been prescribed both Acyclovir and Tizanidine, do not start, stop, or change either medication on your own — some medicines are unsafe to stop suddenly. Tell your prescriber and pharmacist that you take both so they can decide whether the combination is right for you, adjust the dose, monitor you more closely, or suggest an alternative.
This information is educational — not medical advice.
This page is provided for general educational purposes and summarizes publicly available data from sources such as the U.S. Food & Drug Administration. It is not a substitute for the judgment of a licensed clinician and should not be used to start, stop, or change any medication. It may be incomplete or out of date, and individual circumstances vary. Always talk with your prescriber or pharmacist about your specific medications and health conditions. If you think you may have a medical emergency, call 911.