Last reviewed: October 2026
Twenty percent. That is the figure printed in the Neurontin prescribing information, and it is why the topic of gabapentin and antacids deserves more than a shrug. Most “don’t mix it with antacids” warnings you hear at the pharmacy counter are vague or borrowed from other drugs. This one comes with a measured result, a named product, and a specific timing recommendation. That makes it unusually easy to check, which is exactly what this article is built for: a short account of what the label actually found, followed by a numbered list of things to confirm with your pharmacist, one item at a time.
Nothing here replaces your own prescription instructions. Gabapentin comes in several products that behave differently, so the goal is simply to help you arrive at the pharmacy with the right questions written down.
Key takeaways before you start the checklist
1. In a study cited on the Neurontin label, an aluminum hydroxide/magnesium hydroxide antacid (Maalox) lowered average gabapentin absorption by about 20% when the two were taken together, and by about 10% when gabapentin was taken 2 hours later.
2. The label recommends taking gabapentin at least 2 hours after Maalox.
3. Neurontin, Gralise and Horizant are not interchangeable, and their labels say different things about antacids.
4. Calcium-carbonate-only products such as Tums are not named in the gabapentin labels reviewed here, so ask rather than assume.
5. The bigger safety issue with gabapentin is drowsiness and, with opioids or other sedating drugs, slowed breathing.
The finding: what the label measured about gabapentin and antacids
The source for the whole topic is the Neurontin prescribing information on the FDA website (revised April 2025). In its drug interaction and clinical pharmacology sections, the label describes a small study of 16 people. When gabapentin was taken at the same time as Maalox, an antacid containing aluminum hydroxide and magnesium hydroxide, the average amount of gabapentin that reached the bloodstream dropped by about 20%.
The same study looked at spacing. When gabapentin was taken 2 hours after the Maalox dose, the drop shrank to about 10%. Based on that, the label recommends that gabapentin be taken at least 2 hours following Maalox. The Neurontin Medication Guide, the handout written for patients, turns this into plain instructions: if you take an antacid that contains both aluminum and magnesium, wait at least 2 hours before your next gabapentin dose. It lists Maalox, Mylanta, Gelusil, Gaviscon and DiGel as examples.
Three details matter.
- The direction matters. The study and the recommendation are about antacid first, gabapentin second. The label does not describe what happens when the order is reversed, so that question belongs on your list for the pharmacist.
- Twenty percent is an average. Some people in a study lose more, some less. It is not a prediction of what will happen to you on any given day.
- The label doesn’t call this dangerous. A lower level of gabapentin isn’t a toxic reaction. The concern is that, if it happens repeatedly, your medicine may work less well than your prescriber expects, which matters most for people taking gabapentin for seizures.
Other references echo the rule. MedlinePlus’s gabapentin page tells readers who use antacids such as Maalox or Mylanta to take them at least 2 hours before gabapentin tablets, capsules or solution,, and the NIH StatPearls review of gabapentin agrees.
The verification checklist: six things to confirm with your pharmacist
Work through these in order. Each item names what to look at, what the labels say, and the exact question worth asking. Screenshot this section or jot the numbers down for your next refill.
Check 1: Which gabapentin product do I actually have?
Everything else depends on this. “Gabapentin” on a pharmacy label can mean one of three quite different things, and the antacid language changes between them.
Immediate-release gabapentin (Neurontin and its generics). This is the most common form: capsules (100, 300 and 400 mg), tablets (600 and 800 mg) and an oral solution. For adults and teens 12 and older, the Neurontin label describes dosing three times a day and states that the maximum time between doses should not exceed 12 hours. It can be taken with or without food. This is the product the 20% study applies to directly, and its Medication Guide carries the 2-hour antacid instruction.
Gralise (once-daily gabapentin). Gralise is an extended-release gabapentin tablet approved for postherpetic neuralgia, the nerve pain that can follow shingles. The Gralise prescribing information directs it to be taken once daily with the evening meal and swallowed whole, and states that it is not substitutable with other gabapentin products. Its antacid paragraph cites the immediate-release data (about a 20% reduction when taken together, and, in its wording, only about 5% when gabapentin was taken 2 hours after the antacid) and recommends taking Gralise at least 2 hours after an aluminum/magnesium antacid. Note the small difference: the Neurontin label reports about 10% at the 2-hour mark, while the Gralise label reports about 5%. Both point to the same 2-hour spacing.
Horizant (gabapentin enacarbil). Horizant isn’t gabapentin itself. It is a prodrug, a molecule the body converts into gabapentin after absorption, in an extended-release tablet. The Horizant prescribing information lists two adult uses: moderate-to-severe primary restless legs syndrome (RLS) and postherpetic neuralgia. For RLS, the label’s dose is taken once daily at about 5 PM with food. It too is not substitutable with other gabapentin products. When I searched the full Horizant prescribing information, I found no antacid or Maalox statement; the interaction studies it describes involve cimetidine, naproxen and morphine, plus a warning about alcohol speeding up release from the tablet.
What to confirm: “Is my prescription immediate-release gabapentin, Gralise, or Horizant? And does my product’s label say anything about antacids?” Your pharmacy label and the manufacturer name on the bottle usually answer the first part in seconds.
| Product | How the label says to take it | Antacid language on the label |
|---|---|---|
| Neurontin / generic immediate-release gabapentin (capsules, tablets, solution) | Usually three times a day (adults); with or without food; no more than 12 hours between doses | About 20% lower absorption with Maalox taken together; take gabapentin at least 2 hours after Maalox |
| Gralise (gabapentin extended-release) | Once daily with the evening meal; swallow whole | Cites the immediate-release data; take Gralise at least 2 hours after an aluminum/magnesium antacid |
| Horizant (gabapentin enacarbil extended-release) | RLS: once daily at about 5 PM with food; swallow whole, don’t cut, crush or chew | No antacid statement found in the prescribing information reviewed |
Check 2: Does my antacid contain aluminum or magnesium?
The tested product was an aluminum hydroxide/magnesium hydroxide combination, and the Medication Guide frames its warning around antacids containing aluminum and magnesium. So the second box to tick is the Active Ingredients line in the Drug Facts panel on your antacid package. Brand names alone are not reliable, because the same brand often sells several formulas with different ingredients.
- Maalox and Mylanta liquids: traditional formulas pair aluminum hydroxide with magnesium hydroxide, often with simethicone for gas. Some newer versions under these names use different ingredients, so read the panel.
- Gaviscon: US products commonly combine aluminum hydroxide with magnesium carbonate or magnesium trisilicate. It is named in the Neurontin Medication Guide.
- Rolaids: many Rolaids products combine calcium carbonate with magnesium hydroxide. That means magnesium is present even though the main ingredient is calcium.
- Milk of magnesia: this is magnesium hydroxide, usually used as a laxative but also as an antacid. It isn’t named in the gabapentin label, but it contains one of the two tested ingredients, so ask.
What to confirm: bring the box or a photo of its Drug Facts panel and ask: “Does this antacid fall under the 2-hour rule for my gabapentin?”
Check 3: What about Tums and other calcium-carbonate-only products?
This is where people most often get conflicting answers, and the honest reason is that the labels are silent. The Neurontin study used an aluminum/magnesium product. The Medication Guide’s list of examples doesn’t include Tums, and the Gralise and Horizant labels reviewed here don’t mention calcium carbonate antacids either. No measured number exists in these labels for calcium carbonate on its own.
Silence isn’t proof that nothing happens; it means no study was reported. Some pharmacists space all antacids as a cautious habit; others are comfortable with calcium carbonate closer to a dose. Your pharmacist knows your full medication list, which may change the advice. Calcium carbonate has well-known interactions with some antibiotics and thyroid medicine, so spacing you already use for those may end up covering gabapentin too.
What to confirm: “My antacid is calcium carbonate only. Do you want me to space it from gabapentin anyway, and by how much?” Write the answer down so you don’t have to ask again at the next refill.
Check 4: What about H2 blockers and PPIs such as famotidine or omeprazole?
Many people use acid reducers instead of, or along with, antacids. An antacid neutralizes acid already in the stomach; H2 blockers (famotidine, cimetidine) and proton pump inhibitors (omeprazole, pantoprazole and others) reduce how much acid the stomach makes.
The only acid reducer the gabapentin labels describe studying is cimetidine, an older H2 blocker. The Neurontin label reports that cimetidine taken four times a day lowered the apparent clearance of gabapentin by 14% and lowered creatinine clearance by 10%. In plain terms, cimetidine slightly slowed how fast the kidneys cleared gabapentin from the body, so levels ran a little higher, not lower. The label says this effect is not expected to be clinically important. The Gralise label repeats the same numbers with the same conclusion. Horizant’s label describes its own cimetidine study, in which gabapentin exposure rose about 24% and renal clearance fell about 20%, and again calls this not clinically relevant.
That is a different mechanism from the antacid effect: cimetidine acts on removal by the kidneys, while Maalox means less drug absorbed. The labels reviewed here describe no studies with famotidine or proton pump inhibitors. One wrinkle: some heartburn products pair an acid reducer with an antacid in the same tablet, so show the package rather than going by brand name.
What to confirm: “I take [name of acid reducer]. Does it need spacing from gabapentin, and does the product I bought also contain an antacid?” Also mention any kidney problems, since gabapentin leaves the body through the kidneys and kidney function affects dosing far more than any heartburn medicine does.
Check 5: How do I fit a 2-hour gap into a three-times-a-day schedule?
Immediate-release gabapentin is often taken three times a day, leaving gaps of several hours between doses. Heartburn doesn’t follow a timetable, so the goal is to know in advance where an antacid fits, rather than doing math at midnight.
The table below uses made-up example times only. It isn’t a recommended schedule and says nothing about how much gabapentin to take. Your prescriber sets your dose times, and your pharmacist can help you map antacid windows onto them.
| Example gabapentin dose time | If an aluminum/magnesium antacid is taken… | What the label pattern suggests | Question for your pharmacist |
|---|---|---|---|
| 8:00 AM | At 6:00 AM or earlier | Matches the “gabapentin at least 2 hours after antacid” pattern | Is an early-morning antacid fine with my morning dose? |
| 8:00 AM | At 7:30 AM | Less than 2 hours before the dose; not the pattern the label recommends | Should I delay the dose, or is a short delay a bad idea for my condition? |
| 2:00 PM | At 10:00 AM to noon | Mid-morning antacid sits at least 2 hours before the afternoon dose | Is mid-morning my safest window for heartburn relief? |
| 10:00 PM | At 8:00 PM, after dinner | Exactly 2 hours before the bedtime dose | Is 2 hours enough, or do you suggest a longer gap? |
| 10:00 PM | At 11:30 PM, for reflux after lying down | Antacid after gabapentin; the label didn’t study this order | Does the reverse order matter for me? |
A few principles keep this from getting complicated.
- Don’t stretch the dosing gap to make room. The Neurontin label says the time between doses shouldn’t exceed 12 hours. Shuffling gabapentin later and later to fit antacids can push you past that, and for people with seizures in particular, gaps matter.
- Don’t double up to make up for an antacid. Taking extra gabapentin because you think the antacid “cancelled” some of the dose isn’t something the label supports, and it adds to drowsiness and dizziness.
- If timing goes wrong and a dose gets skipped, follow your product’s missed-dose instructions. Our guide to what to do after a missed gabapentin dose walks through what the patient information says for each product.
- For Gralise, the once-daily dose goes with the evening meal. If you usually take an aluminum/magnesium antacid right after dinner, that collides with the label’s 2-hour recommendation. Ask whether an earlier antacid or a different heartburn plan fits better.
- For Horizant, the RLS dose is around 5 PM with food. Its label doesn’t carry an antacid statement, but you can still ask the pharmacist whether they want any spacing.
What to confirm: bring your actual dose times and ask the pharmacist to mark one or two “antacid windows” on your schedule. Then keep that note with your pill organizer.
Check 6: Bedtime doses and nighttime reflux
Night is when the gabapentin and antacids question usually becomes real. Reflux worsens after lying down, many schedules include a bedtime dose, and gabapentin’s drowsiness makes it likelier you’ll wake up foggy and reach for whatever is on the nightstand.
Consider three common situations to raise with your pharmacist:
- Heartburn right before the bedtime dose. The label pattern favors taking the antacid first and the gabapentin at least 2 hours later. That may not suit your sleep, so ask whether a different heartburn option before bed is more practical.
- Waking with reflux after the bedtime dose. Here the antacid comes after gabapentin, an order the label doesn’t describe. Ask whether this matters for you, especially if it happens often.
- Getting up at night while drowsy. Gabapentin can cause sleepiness and dizziness, and the Medication Guide warns this can raise the chance of falls. Keep the path to the bathroom or kitchen clear and lit, and sit on the edge of the bed for a moment before standing.
Needing an antacid most nights isn’t something to work around forever; frequent reflux deserves its own look from your prescriber. And if what you feel is more queasiness than burning, the cause may differ; our post on gabapentin and nausea covers what the labels report and what to ask.
What to confirm: “What should I do for heartburn at night that won’t interfere with my bedtime gabapentin dose?”
Why gabapentin absorption has a ceiling, in plain English
To see why a 10% or 20% drop gets attention, it helps to know something unusual about immediate-release gabapentin. Most pills are absorbed roughly in proportion to dose. Gabapentin isn’t.
The Neurontin label states plainly that gabapentin bioavailability is not dose proportional; as the dose goes up, the fraction absorbed goes down. It gives approximate figures for total daily doses split into three portions:
| Total daily dose (given in 3 divided doses) | Approximate bioavailability |
|---|---|
| 900 mg/day | 60% |
| 1200 mg/day | 47% |
| 2400 mg/day | 34% |
| 3600 mg/day | 33% |
| 4800 mg/day | 27% |
Picture the intestinal wall with a limited number of turnstiles that let gabapentin through. At low doses most molecules find an open one; at higher doses they’re busy and more drug passes by unabsorbed. StatPearls describes this as possibly due to saturation of the transporter at clinical doses. That is the reason immediate-release gabapentin is split into several doses across the day rather than given all at once.
The antacid effect stacks on top of this. Your prescriber chooses a dose knowing the absorption ceiling exists. If an antacid then trims what does get absorbed, by an amount that can vary from dose to dose depending on timing, the level in your blood becomes less predictable. That is why the label suggests consistent spacing rather than simply saying “antacids are fine.” The label doesn’t explain the exact chemistry of how Maalox lowers absorption, and I won’t guess at it here.
The other two products work differently, which is part of why they aren’t interchangeable:
- Gralise is designed to stay in the stomach longer and release gabapentin slowly with a meal. Its label says food increases both the rate and extent of absorption, and that taking it on an empty stomach substantially lowers bioavailability. That’s why the evening meal is part of the instructions.
- Horizant sidesteps the turnstile problem. As a prodrug, gabapentin enacarbil is absorbed through different, higher-capacity transporters (the label names MCT-1), which its label says are not saturated at high doses. As a result, Horizant’s label describes gabapentin exposure as approximately dose-proportional across a wide range.
This also explains Check 1: the antacid study used immediate-release gabapentin, so applying its numbers to other products is an extrapolation.
Safety checks that matter more than antacid timing
A slight drop in absorption is manageable. These issues are more serious, and they apply to every gabapentin product.
Breathing problems with opioids and other sedating drugs
In December 2019, the FDA issued a drug safety communication about gabapentinoids (Neurontin, Gralise, Horizant, and pregabalin products) warning that serious breathing difficulties can occur in people with respiratory risk factors. The higher-risk groups it named were people taking opioid pain medicines or other central nervous system depressants, people with conditions that reduce lung function such as COPD, and older adults. The current labels for all three gabapentin products carry a respiratory depression warning.
Many people who take gabapentin for nerve or back pain also take an opioid at some point. If that’s you, our article on tramadol for back pain is a useful companion read. Benzodiazepines are another common combination; the differences between two of them are covered in our lorazepam vs Klonopin comparison. Alcohol counts too. The FDA advised patients to tell their health care professional about all medicines and substances they use, including alcohol.
Get emergency help right away if someone taking gabapentin shows signs the FDA listed, including:
- confusion or disorientation
- unusual dizziness or lightheadedness
- extreme sleepiness or lethargy
- slowed, shallow, or difficult breathing
- being hard to wake or not responding normally
- bluish skin, especially on the lips, fingers or toes
Drowsiness and dizziness
Sleepiness and dizziness are among the most common gabapentin side effects, and the Neurontin label gives them their own warning. The Medication Guide advises not driving or operating heavy machinery until you know how gabapentin affects you, and not drinking alcohol or taking other medicines that make you sleepy or dizzy without talking to your prescriber. Falls and accidents from these effects cause far more real harm than any antacid interaction.
Mood changes and suicidal thoughts
Like other antiepileptic drugs, gabapentin carries a warning about suicidal behavior and ideation. Watch for new or worsening depression, anxiety, irritability, unusual mood or behavior changes, or thoughts of self-harm, and report them to the prescriber promptly. If someone is in immediate danger, call 911, or call or text 988 for the Suicide and Crisis Lifeline.
Other points to keep on your radar
- Don’t stop suddenly. The Medication Guide says not to stop gabapentin without talking to your prescriber first. Stopping abruptly can cause problems, including seizures in people who take it for epilepsy.
- Serious allergic and skin reactions. The label warns about a multiorgan hypersensitivity reaction (DRESS) and about anaphylaxis and angioedema. Rash, fever, swollen glands, or swelling of the face, lips or throat need prompt medical attention.
- State rules. Gabapentin isn’t a federally controlled substance, but several states schedule it or track it in prescription monitoring programs. That can affect how refills are handled where you live.
- Overdose. If too much is taken, the Medication Guide says to get medical help or contact Poison Control at 1-800-222-1222.
Putting it in the context of why you take gabapentin
How strict to be about spacing gabapentin and antacids depends partly on what you’re treating. For partial seizures, steady blood levels are a priority. For nerve pain, small swings may be less noticeable, though consistency still helps your prescriber judge whether the dose works. With neuropathy, gabapentin is usually one part of a broader plan; our guide to neuropathy treatment for the legs and feet, including home measures covers the non-drug pieces worth discussing with your care team.
If your prescription is Horizant for restless legs syndrome, the antacid question is mostly a non-issue on the current label, and timing your dose around 5 PM with food is the main instruction to follow. For quick comfort measures during an RLS flare, see how to stop restless legs right away, and talk with your prescriber if symptoms keep breaking through.
Gabapentin and antacids: questions readers send in
Is a 20% drop in absorption enough to make my gabapentin stop working?
Not usually from a single occasional dose. The 20% figure is an average from a small study where gabapentin and Maalox were taken together. The concern is repeated, unpredictable reductions over time, which could leave your levels lower than your prescriber intended. If you use an aluminum/magnesium antacid regularly, ask your pharmacist how to space it consistently.
Does the 2-hour rule work in both directions?
The label’s recommendation is specifically to take gabapentin at least 2 hours after Maalox. It doesn’t describe a study with the antacid taken after gabapentin. Some pharmacists suggest spacing both ways as a simple habit. Ask what they recommend for your schedule.
Why does the Gralise label say 5% at 2 hours when Neurontin says 10%?
Both labels describe the reduction seen with immediate-release gabapentin taken 2 hours after an aluminum/magnesium antacid, but they report the figure differently: about 10% on the current Neurontin label and about 5% on the Gralise label. The practical recommendation is the same on both: take the gabapentin product at least 2 hours after the antacid.
I switched from generic gabapentin to Horizant. Do I still need to space my Maalox?
The Horizant prescribing information reviewed for this article doesn’t include an antacid statement. Horizant is absorbed by a different route than regular gabapentin. Still, confirm with your pharmacist, especially since Horizant is not interchangeable with other gabapentin products and your instructions changed with the switch.
Do magnesium supplements count as an antacid here?
The gabapentin labels speak about antacids, not supplements. But many magnesium supplements are magnesium oxide or hydroxide, the same family of compounds found in some antacids. Since the labels don’t settle the question, show your supplement bottle to the pharmacist and ask whether to space it.
My heartburn started after I began gabapentin. Is that related?
Stomach effects such as nausea are reported with gabapentin, but new heartburn has many possible causes. Tell your prescriber rather than adding antacids indefinitely.
References
- Pfizer / Viatris. Neurontin (gabapentin) prescribing information and Medication Guide. US Food and Drug Administration. Revised April 2025.
- Gralise (gabapentin) extended-release tablets prescribing information. Drugs.com (FDA label text). Accessed October 2026.
- Horizant (gabapentin enacarbil) extended-release tablets prescribing information. Drugs.com (FDA label text). Revised April 2025.
- US Food and Drug Administration. Neurontin, Gralise, Horizant (gabapentin) and Lyrica, Lyrica CR (pregabalin): Drug Safety Communication – serious breathing difficulties. December 19, 2019.
- MedlinePlus. Gabapentin. National Library of Medicine.
- Yasaei R, Katta S, Saadabadi A. Gabapentin. StatPearls, NCBI Bookshelf. Updated February 2024.
This article is for general information and isn’t a substitute for advice from your prescriber or pharmacist. Gabapentin products differ, and only someone who knows your full medication list and health history can tell you how to time antacids or other medicines with your dose. Don’t change, skip or stop any medication without talking to your prescriber first. If you have questions about this article, you can reach our team through the Mediclox contact page.