Why does GTN cream cause headaches?

GTN is a vasodilator — it works by widening blood vessels. The same mechanism that relaxes the internal sphincter muscle and improves blood flow to the fissure also affects blood vessels elsewhere in the body, including in the head. This is what causes the headache. It is a known and expected effect of how the medication works, not a sign that something is wrong.

How long do GTN headaches last?

Most people report that headaches begin within minutes of applying the cream and last anywhere from 20 minutes to a few hours. For many people, the headaches become less intense over the first one to two weeks of use as the body adjusts. Some people find them manageable from the start; others find them difficult throughout the course.

Can I take paracetamol for GTN headaches?

Many people describe taking simple pain relief their pharmacist has approved shortly before applying GTN. Check first which pain relief is appropriate alongside your specific treatment, because the answer depends on what else you take.

What if I cannot tolerate the headaches from GTN?

If headaches are severe or not improving after the first week or two, talk to your doctor. They may suggest adjusting how much you apply, trying a different application technique, or switching to a different topical treatment like diltiazem, which tends to cause fewer headaches. Do not stop treatment on your own without discussing it with your doctor first.

Is GTN the same as Rectogesic?

Yes. Rectogesic is a brand name for GTN (glyceryl trinitrate) ointment, commonly used in the UK and Australia. The same side effects and management strategies described on this page apply to Rectogesic.

GTN cream side effects and headaches

Published 12 March 2026 ·Last reviewed 12 March 2026 by the editorial team ·How we create our content

At a glance

GTN (glyceryl trinitrate) cream is one of the most commonly prescribed topical treatments for anal fissures. It works by relaxing the internal sphincter muscle, improving blood flow to the fissure, and giving it a better chance to heal. It is effective for many people — but its side effects, particularly headaches, are the single most discussed aspect of using it.

This page focuses specifically on GTN side effects: what people report, why headaches happen, practical strategies for managing them, and when it makes sense to talk to your doctor about alternatives.

Why GTN causes headaches

GTN is a vasodilator. It widens blood vessels. That is how it works on the fissure — by increasing blood flow to the area and relaxing the sphincter muscle.

The problem is that this effect is not limited to the anal area. When GTN is absorbed, it affects blood vessels throughout the body, including those in the head. The widening of blood vessels in the brain is what causes the headache.

This is not an allergic reaction or a sign that the medication is harming you. It is a predictable pharmacological effect. Knowing this does not make the headaches less uncomfortable, but it can help to understand that they are expected and that most people find they improve over time.

What people report about GTN headaches

Headaches come up in nearly every conversation about GTN. The experience varies significantly from person to person.

Intensity

Some people describe mild headaches — a dull pressure that is noticeable but does not interfere with their day
Others describe throbbing, intense headaches that make it difficult to function
A smaller group reports headaches severe enough that they cannot continue the treatment
Most people fall somewhere in the middle

Timing

Headaches typically begin within five to fifteen minutes of applying the cream
They usually peak within the first 30 minutes
Duration ranges from 20 minutes to several hours
Evening applications may cause headaches that are less disruptive because people can rest through them

Do they get better?

This is the question everyone asks. The answer, based on what people consistently report:

For many people, yes. Headaches often become noticeably less severe after the first one to two weeks of regular use. The body appears to adjust to the vasodilating effect.
For some people, they remain difficult. A portion of people do not see meaningful improvement in headaches even after two weeks.
The first few applications are usually the worst. People frequently describe the first three to five days as the hardest, with gradual improvement after that.

Other GTN side effects

Headaches get the most attention, but GTN can cause other side effects as well.

Dizziness and lightheadedness

Particularly common when standing up quickly after applying the cream
The vasodilating effect can temporarily lower blood pressure
People report that lying down for 10 to 15 minutes after application helps
This side effect is usually mild and temporary

Flushing

A warm feeling or redness in the face or upper body
Happens because blood vessels near the skin surface widen
Usually brief and harmless
More noticeable in the first few days of use

Local irritation

Some people report a mild burning or stinging sensation when applying the cream
This is usually brief and settles within minutes
It is distinct from fissure pain — more of a surface sensation
If irritation is severe or worsening, mention it to your doctor

Heart rate changes

Some people notice a slight increase in heart rate after application
This is related to the vasodilating effect and is usually mild
If you experience significant palpitations or racing heart, contact your doctor

Practical strategies people share

These come from what people describe in their own accounts. They are not medical instructions — always follow your doctor’s guidance about how to use your prescribed treatment.

Timing your application

Before bed is the most popular strategy. Headaches are less disruptive when you can lie down and sleep through the worst of them.
After a sitz bath — the warm water may help with absorption and some people find the relaxation offsets the headache slightly
When you can rest for 20 to 30 minutes — avoiding strenuous activity right after application helps with both headaches and dizziness

Managing the headache

Some people report that taking paracetamol 20 to 30 minutes before applying GTN reduces the headache severity — discuss this approach with your doctor or pharmacist
Staying hydrated may help, as dehydration can worsen headaches
A cool flannel on the forehead during the worst of it
Darkening the room if the headache involves light sensitivity

Application technique

Use a small amount — more cream does not mean faster healing, but it can mean worse headaches. Apply only the amount your doctor has instructed.
Use a finger cot or glove — this prevents the GTN from absorbing through your finger, which can contribute to headaches
Wash hands thoroughly after application, even if you wore a glove. GTN residue on hands can cause headaches if you touch your face or other skin
Apply to the area directed — your doctor will explain where to apply it. The goal is local absorption, not widespread coverage

Reducing absorption

People describe finding a balance between applying enough to be effective and not so much that side effects are overwhelming
Some people report that their doctor adjusted the amount or frequency when side effects were difficult
Never adjust your dose on your own — talk to your doctor if side effects are not manageable

When to talk to your doctor about switching

GTN works well for many people, but the headaches are a legitimate reason to discuss alternatives. Consider talking to your doctor if:

Headaches have not improved after two weeks of consistent use
The headaches are severe enough that you are skipping applications
You experience fainting or near-fainting episodes
Side effects are significantly affecting your quality of life
You cannot maintain the prescribed application schedule because of side effects

The most common alternative is diltiazem cream, which works by a different mechanism and typically causes fewer headaches. Switching is a routine part of fissure treatment — it does not mean treatment has failed, just that a different approach may suit you better.

GTN and breastfeeding

This is a question that comes up specifically for people who developed a fissure during or after pregnancy. GTN is a medication that is absorbed into the body, and people understandably worry about whether it could affect breast milk.

This is a conversation to have directly with your doctor. They can advise on whether GTN is appropriate for your situation or whether an alternative treatment would be better while you are breastfeeding. Do not start or stop any medication without discussing it with your prescriber.

Completing the course

One of the most important things people report about GTN is the temptation to stop early — either because headaches are difficult, or because the fissure starts feeling better.

Both of these are understandable, but stopping early is one of the most common reasons for fissures not fully healing. A typical course is six to eight weeks, and completing it gives the fissure the best chance to close completely.

If you are struggling with side effects, talk to your doctor rather than stopping on your own. They can help you find a way to continue effectively — whether that means adjusting how you use GTN or switching to a different treatment.

Questions to ask your prescriber

What should I do if the headaches do not improve after the first week or two?
Is there a specific amount I should be using, and could adjusting it reduce side effects?
When should I contact you about side effects versus managing them at home?
What are my options if I cannot tolerate GTN?
Should I continue conservative care (fibre, sitz baths, hydration) alongside this treatment?

If you experience severe dizziness or fainting after applying GTN, a headache that does not respond to paracetamol or is severe, heavy or persistent rectal bleeding, or symptoms that are worsening rather than improving, seek medical care.