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.