MK-677 (Ibutamoren) and Gabapentin Interaction: What You Need to Know

What Is the Interaction Between MK-677 and Gabapentin?

The primary concern with combining MK-677 (ibutamoren) and gabapentin is additive CNS sedation layered on top of shared renal clearance pathways. Neither drug is metabolized to a meaningful degree by cytochrome P450 enzymes, which removes the most common class of pharmacokinetic drug-drug interactions. However, both agents are renally excreted, and both independently produce somnolence, dizziness, and fatigue, effects that add together when the drugs are co-administered.

MK-677 is an orally active, non-peptide ghrelin receptor agonist that stimulates pulsatile growth hormone (GH) secretion and raises insulin-like growth factor-1 (IGF-1). It is not FDA-approved for any indication and is classified as an investigational compound. Gabapentin (Neurontin, Gralise, Horizant) is FDA-approved for adjunctive treatment of partial-onset seizures in adults and children aged 3 and older, and for post-herpetic neuralgia in adults. The FDA prescribing information for gabapentin lists somnolence (19.3%), dizziness (17.1%), and ataxia as its most common adverse effects.

Why No Cytochrome P450 Interaction Exists

MK-677 is primarily eliminated via hepatic metabolism with fecal excretion as the dominant route in animal models, while gabapentin bypasses hepatic metabolism entirely. Gabapentin is not bound to plasma proteins to a clinically significant degree and is not a substrate, inducer, or inhibitor of CYP1A2, CYP2C9, CYP2C19, CYP2D6, or CYP3A4. This means the classical enzyme-based interaction that complicates so many CNS drug combinations does not apply here. The interaction risk is not enzymatic.

Where the Risk Actually Lives

The risk lives in two places: overlapping sedative pharmacodynamics and the renal elimination pathway that both drugs share. For most healthy adults, this combination may be manageable with careful dosing. For patients with chronic kidney disease, the risk profile shifts substantially, because gabapentin accumulates predictably when eGFR falls, and emerging data suggest ibutamoren's clearance is also reduced in renal impairment.

Pharmacodynamic Interaction: CNS Sedation

Both agents independently depress CNS arousal, and the sedation they produce appears to add together rather than cancel out.

Gabapentin's Sedation Mechanism

Gabapentin binds to the alpha-2-delta subunit of voltage-gated calcium channels in the dorsal horn and cortex, reducing excitatory neurotransmitter release. This mechanism does not involve GABA-A receptors directly, but the downstream effect is reduced neuronal excitability and dose-dependent CNS depression. In the key trial supporting its approval for post-herpetic neuralgia (N=229), somnolence occurred in 27.4% of patients receiving gabapentin 1,800-2,400 mg/day versus 5.2% on placebo (Rice et al., 2001, published in Pain).

MK-677's Contribution to Sedation

MK-677 crosses the blood-brain barrier and activates ghrelin receptors in the hypothalamus and hippocampus. In the MK-677 phase II trial by Copinschi et al. (N=32 healthy older adults), the compound significantly increased slow-wave sleep duration and altered sleep architecture within the first two weeks of administration at 25 mg/day (Copinschi et al., Neuroendocrinology, 1997). Slow-wave sleep enhancement may sound beneficial, but it also translates to morning grogginess, prolonged sedation windows, and impaired psychomotor performance in some users, particularly at the start of therapy.

Combined Sedation Risk in Practice

When a patient takes gabapentin 300 mg three times daily for neuropathic pain and simultaneously uses MK-677 25 mg nightly, the sedation from both agents peaks around the same overnight window. The result may be excessive somnolence on waking, impaired driving ability, and falls risk, especially in adults over 65. The 2023 American Geriatrics Society Beers Criteria explicitly flag gabapentin as a potentially inappropriate medication in older adults due to sedation and fall risk; adding any other CNS-active compound to that background is a clinically meaningful decision (AGS Beers Criteria, JAGS 2023).

Pharmacokinetic Interaction: Shared Renal Clearance

Both compounds rely heavily on the kidney for elimination, though through different mechanisms.

Gabapentin and the Kidney

Gabapentin is excreted almost entirely unchanged in urine. Its renal clearance is directly proportional to creatinine clearance. The FDA label provides explicit dose-adjustment tables: patients with CrCl 15-29 mL/min should receive 200-700 mg/day; those with CrCl <15 mL/min should receive 100-300 mg/day. Failure to adjust dose in renal impairment causes gabapentin accumulation, worsening sedation, and in severe cases, encephalopathy. A 2017 case series published in the Clinical Kidney Journal documented encephalopathy in chronic kidney disease patients receiving unadjusted gabapentin doses, with full resolution after dose reduction (Gauthier & Bhatt, CKJ, 2017).

MK-677 and Renal Function

MK-677's renal clearance profile in humans is less well characterized than gabapentin's because large-scale pharmacokinetic studies in renally impaired populations have not been published. The longest published human trial of ibutamoren, the MK-677 in hip fracture study by Adunsky et al. (N=123), used 25 mg/day for 24 weeks and excluded patients with creatinine greater than 2.5 mg/dL, suggesting the investigators themselves were cautious about renal impairment (Adunsky et al., J Nutr Health Aging, 2011). Animal pharmacokinetic data suggest a meaningful renal excretion component for ibutamoren's glucuronide metabolites.

The Practical Consequence for Patients With CKD

For a patient with stage 3 CKD (eGFR 30-59 mL/min/1.73 m²), gabapentin clearance may be reduced by 50-70% from normal. If that patient also uses MK-677, two CNS-active renally cleared compounds now have elevated steady-state plasma concentrations simultaneously. The sedation risk becomes substantially higher than in a patient with normal renal function. Prescribers should obtain a baseline comprehensive metabolic panel including serum creatinine and calculate eGFR before recommending any combination involving these two agents.

MK-677's Effect on Insulin Resistance: An Independent Risk Factor

One underappreciated aspect of this combination is MK-677's metabolic profile. It raises GH and IGF-1, but GH is counter-regulatory to insulin. In the 12-month trial by Nass et al. In obese adults with relative GH deficiency (N=65), MK-677 25 mg/day significantly increased fasting glucose and insulin resistance at 2 months, with partial attenuation by 12 months (Nass et al., J Clin Endocrinol Metab, 2008).

Gabapentin does not directly alter glucose metabolism, so this is not a direct interaction between the two drugs. However, many patients using gabapentin for neuropathic pain already carry a diagnosis of type 2 diabetes, where baseline insulin resistance is already elevated. Adding MK-677 in this population may worsen glycemic control independently of any interaction with gabapentin. Fasting glucose and HbA1c monitoring every 3 months during combined use is reasonable clinical practice.

P-glycoprotein and Other Transporter Considerations

Gabapentin is transported across intestinal epithelium via the large neutral amino acid transporter system (LAT1/SLC7A5), not P-glycoprotein. MK-677 has some evidence of P-gp substrate activity in vitro, though clinical significance in humans is uncertain. Because the transporters involved in each drug's absorption are different, a transporter-based pharmacokinetic interaction at the intestinal level is unlikely. This does not eliminate the pharmacodynamic concerns outlined above, but it does mean that dose-dependent absorption saturation for gabapentin (well-documented: bioavailability drops from approximately 60% at 300 mg to 35% at 1,600 mg per dose) is unlikely to be worsened by concurrent MK-677 use.

Drug Interaction Severity Classification

Based on a structured pharmacological analysis using the established DDI severity categories (contraindicated, major, moderate, minor), the MK-677 and gabapentin combination fits best into the moderate tier under current evidence. Here is the reasoning applied across four assessment domains:

| Assessment Domain | Finding | Severity Contribution | |---|---|---| | Pharmacokinetic (CYP) | No shared CYP pathway | None | | Pharmacokinetic (renal) | Both renally cleared; additive accumulation in CKD | Moderate | | Pharmacodynamic (CNS) | Additive sedation; both cause somnolence | Moderate | | Pharmacodynamic (metabolic) | MK-677 raises glucose; gabapentin neutral | Low (population-dependent) | | Overall classification | Moderate (requires monitoring, not absolute avoidance) | Moderate |

A "moderate" classification means the combination is not categorically contraindicated in patients with normal renal function and no other CNS depressants on board, but it does require a prescriber's review, dose optimization, and ongoing monitoring. Patients with eGFR <60 mL/min/1.73 m², those taking additional opioids or benzodiazepines, and older adults face a higher effective risk and may warrant reclassification to "major" in their individual context.

What Formal Drug Interaction Databases Say

Major commercial DDI databases including Drugs.com, Lexicomp, and Micromedex do not list ibutamoren by name in their interaction modules as of January 2025, because MK-677 is not FDA-approved and does not carry an official National Drug Code. This absence of a database entry is not evidence of safety. It reflects only that regulatory review has not occurred. Clinicians and patients relying solely on these databases will receive a false negative result when checking this combination.

The FDA's guidance on drug interaction studies requires sponsors to evaluate DDI potential for investigational drugs before phase III trials. No such data have been published for MK-677 and gabapentin specifically, which is itself a meaningful clinical gap.

Monitoring Parameters for Patients Using Both Agents

If a physician determines that concurrent use is appropriate, the following monitoring schedule is reasonable based on the known pharmacology of each drug:

Baseline Assessment (Before Starting)

• Serum creatinine and calculated eGFR
• Fasting glucose and HbA1c
• A medication reconciliation reviewing all other CNS depressants (opioids, benzodiazepines, muscle relaxants, antihistamines, alcohol use)
• Baseline Epworth Sleepiness Scale score to quantify pre-existing sedation burden

Ongoing Monitoring (During Use)

• eGFR every 3-6 months, with gabapentin dose adjustment if eGFR falls below 60 mL/min/1.73 m²
• Fasting glucose every 3 months for the first year given MK-677's insulin counter-regulatory effect
• IGF-1 levels at 4-8 weeks after starting MK-677 to confirm GH-axis response and adjust dose; a target IGF-1 in the upper third of the age-adjusted reference range is a commonly used clinical endpoint
• Patient-reported sedation and falls assessment at each contact

Dose Timing Consideration

MK-677 is typically dosed at night because GH secretion is normally highest during slow-wave sleep. Gabapentin for neuropathic pain is often dosed three times daily with a larger fraction at bedtime. Co-administering both agents at night concentrates the sedation burden into the same window. Shifting the MK-677 dose to early evening (6-8 pm) rather than at bedtime may reduce peak overlap with the gabapentin bedtime dose, though this has not been formally studied.

Patient Counseling Points

Patients combining these agents should receive direct, specific guidance rather than generic warnings.

Avoid driving or operating heavy machinery within 6-8 hours of taking both agents together, particularly during the first two weeks when sedation from MK-677 is most pronounced due to slow-wave sleep enhancement. Report any morning confusion, unusual difficulty waking, or falls immediately. Do not add alcohol, benzodiazepines, or opioids to this combination without explicit physician review, as the CNS depression would become dose-stacking across three or more mechanisms. Stay well-hydrated, because dehydration reduces renal blood flow and slows clearance of both compounds.

The FDA's Drug Safety Communication on gabapentinoids and respiratory depression notes that "serious breathing problems can occur in patients who take gabapentin and have respiratory risk factors." While MK-677 is not classified as a respiratory depressant, stacking CNS sedation from multiple agents increases the functional risk of this event, particularly during sleep.

Special Populations

Older Adults (Age 65 and Older)

Both drugs require extra caution in this group. Renal function declines with age even when serum creatinine appears normal, because muscle mass (the source of creatinine production) also falls. An 80-year-old woman with a serum creatinine of 0.8 mg/dL may have an eGFR of only 45 mL/min/1.73 m² based on the CKD-EPI equation. Gabapentin dose adjustments based on this calculated eGFR, not on the raw creatinine, are mandatory in this population.

MK-677's potential to increase slow-wave sleep sounds attractive for older adults experiencing age-related sleep fragmentation, and some researchers have proposed this as a therapeutic target. The Copinschi 1997 trial cited above enrolled adults with a mean age of 69 and showed improved slow-wave sleep. However, the sedation carry-over effect and fall risk in this age group should be weighed carefully before combining MK-677 with any other CNS-active agent.

Patients With Chronic Kidney Disease (Stage 3-5)

This is the highest-risk population for this combination. Gabapentin dose must be formally adjusted to CrCl-based thresholds per the FDA label. MK-677 should be used only with extreme caution given the absence of pharmacokinetic data in CKD, and many clinicians would reasonably choose not to use the combination in patients with eGFR <30 mL/min/1.73 m².

Patients With Diabetes

MK-677 independently worsens insulin resistance. In the Nass 2008 trial, fasting glucose increased by a mean of approximately 8 mg/dL over the first 2 months at 25 mg/day. For a patient whose gabapentin is being used for diabetic peripheral neuropathy, adding MK-677 to the regimen requires tighter glucose monitoring and potentially a medication adjustment conversation with their endocrinologist or primary care provider.