NAD Precursors Drug-Drug Interaction Table: A Complete Prescriber Reference

What Is the NAD Precursors Drug Class?

NAD precursors are compounds that the body converts into nicotinamide adenine dinucleotide (NAD+), a coenzyme required for over 500 enzyme-catalyzed reactions, including mitochondrial oxidative phosphorylation, DNA repair via PARP enzymes, and sirtuin-mediated gene regulation. Clinically recognized members include niacin (nicotinic acid), nicotinamide (NAM), nicotinamide riboside (NR), nicotinamide mononucleotide (NMN), and tryptophan. Each enters the NAD+ biosynthetic network at a different node, which determines its pharmacology, tolerability, and interaction profile.

Intracellular NAD+ declines with age. A landmark 2013 study by Gomes et al. Published in Cell showed that NAD+ depletion in aged mouse muscle triggered a pseudohypoxic state reversible with NMN supplementation, establishing the rationale for precursor repletion in aging research (1). Human plasma NAD+ metabolomics data from Trammell et al. (2016) confirmed that oral NR 1,000 mg/day raised whole-blood NAD+ by a mean of 2.7-fold over baseline in healthy adults (2).

The Three Biosynthetic Entry Points

Preiss-Handler pathway. Niacin (nicotinic acid) enters here, converting to nicotinic acid mononucleotide (NAMN) via NAPRT1. This route is GPR109A-dependent, which explains the prostaglandin-mediated flushing reaction unique to nicotinic acid.

Salvage pathway. NAM, NR, and NMN all feed NAD+ via NAMPT (the rate-limiting step in the salvage arm). NMN enters downstream of NAMPT, bypassing the rate-limiting enzymatic step entirely. NR requires NRK1/NRK2 phosphorylation to NMN before proceeding (3).

De novo (kynurenine) pathway. Dietary tryptophan is converted through indoleamine 2,3-dioxygenase (IDO) and ultimately quinolinic acid to NAD+. This 60-step route is metabolically inefficient and IDO activity is highly sensitive to cytokine tone, making tryptophan the most pharmacokinetically variable precursor.

Pharmacokinetic Comparisons Across Precursors

| Precursor | Oral bioavailability | Primary route to NAD+ | Half-life (approx.) | |-----------|---------------------|----------------------|---------------------| | Niacin (nicotinic acid) | 60-76% | Preiss-Handler via NAPRT1 | 20-45 min | | NAM (nicotinamide) | ~75% | Salvage via NAMPT | 1-2 h | | NR | ~25% (intact), most cleaved to NAM in gut | Salvage via NRK1/NRK2 | 2.7 h (NAD+ peak) | | NMN | Variable; SLC12A8 transporter-dependent | Salvage downstream of NAMPT | 1-3 h (plasma NMN) | | Tryptophan | ~85% | De novo kynurenine pathway | 1.1 h |

Data compiled from Trammell et al. (2), Airhart et al. (4), and Yoshino et al. (5).

NAD Precursors Drug-Drug Interaction Table

The DDI risk across this class is not uniform. Niacin carries the most well-documented, guideline-flagged interactions. NR and NMN have thinner clinical interaction data, but mechanistic reasoning identifies several co-administration concerns worth documenting in the chart.

Full DDI Reference Table

| NAD Precursor | Interacting Drug / Class | Mechanism | Clinical Effect | Severity | Management | |---|---|---|---|---|---| | Niacin (nicotinic acid) | Statins (simvastatin, lovastatin) | Additive myotoxicity; niacin may inhibit CYP3A4 at high doses, raising statin AUC | Increased myopathy and rhabdomyolysis risk | Contraindicated at niacin >1 g/day with simvastatin >20 mg or lovastatin >20 mg (FDA) | Avoid combination; if lipid benefit needed, use rosuvastatin or pravastatin with close CK monitoring | | Niacin | Warfarin / oral anticoagulants | Niacin inhibits hepatic vitamin K-dependent clotting factor synthesis at >1.5 g/day | INR elevation; bleeding risk | Moderate-Severe | Check INR within 1 week of dose change; titrate warfarin accordingly (6) | | Niacin | Antihypertensives (vasodilators, alpha-blockers) | Additive vasodilation from GPR109A-mediated prostaglandin release | Orthostatic hypotension, syncope | Moderate | Administer niacin with food; avoid co-dosing with vasodilators; monitor sitting/standing BP | | Niacin | Bile acid sequestrants (cholestyramine, colesevelam) | Sequestrant binds niacin in GI tract | Reduced niacin absorption by 30-70% | Moderate | Space doses by at least 4-6 hours; administer niacin first | | Niacin | Sulfonylureas / insulin | Niacin induces insulin resistance via GPR109A-mediated inhibition of adipose lipolysis and downstream FFA signaling | Hyperglycemia; reduced hypoglycemic efficacy | Moderate | Monitor fasting glucose and HbA1c every 3 months; may need antidiabetic dose adjustment (7) | | Niacin | Aspirin (325 mg pre-dose) | COX-1/COX-2 inhibition blunts prostaglandin D2-mediated flush | Reduced flushing (intended effect); minimal DDI risk | Beneficial / Low risk | Standard practice to give aspirin 325 mg 30 min before niacin; avoid in ASA-allergic patients | | Niacin | Alcohol | Additive vasodilation; alcohol increases prostaglandin release | Severe flushing, hypotension | Moderate | Counsel avoidance of alcohol within 2-3 hours of niacin dose | | NAM (nicotinamide) | PARP inhibitors (olaparib, niraparib, rucaparib) | NAM is the primary substrate for PARP enzymes; excess NAM competes with PARP inhibitor binding or replenishes NAD+ to rescue PARP activity | Potential attenuation of PARP inhibitor efficacy in oncology | Moderate (theoretical, mechanistic) | Avoid high-dose NAM (>500 mg/day) in patients on PARP inhibitor therapy pending clinical data (8) | | NAM | Sirtuin-activating compounds (resveratrol, SRT2104) | NAM is a direct SIRT1 inhibitor at intracellular concentrations above ~100 µM | Opposing pharmacodynamic effects on sirtuin-mediated deacetylation | Low-Moderate | Theoretical; no controlled human DDI studies; use caution in combination protocols | | NAM | Carbamazepine | NAM inhibits CYP2C19 and may inhibit CYP3A4 at doses >3 g/day | Elevated carbamazepine plasma levels; toxicity risk | Moderate | Monitor carbamazepine levels; dose adjustment may be needed (9) | | NAM | Primidone | Same CYP inhibition as carbamazepine entry | Elevated primidone and phenobarbital levels | Moderate | Monitor drug levels; consider EEG and clinical toxicity assessment | | NR (nicotinamide riboside) | Statins | NR is cleaved to NAM in the gut; NAM-mediated NAMPT competition with statin-induced CoQ10 depletion may be additive or partially protective | Unclear net effect; NR may partially offset statin-induced mitochondrial NAD+ depletion | Low (theoretical) | No controlled DDI trials; monitor CK if combining with high-dose statins | | NR | Chemotherapy (alkylating agents, platinum compounds) | NR boosts NAD+, which drives PARP-mediated DNA repair, potentially rescuing tumor cells from DNA-damaging agents | Possible attenuation of chemotherapy efficacy | Moderate (preclinical) | Withhold NR during active chemotherapy cycles; restart only after discussion with oncology team (10) | | NMN | CD38 inhibitors (apigenin, quercetin) | CD38 is the primary NAD+-consuming enzyme competing with biosynthesis; inhibiting CD38 synergizes with NMN by reducing NAD+ catabolism | Amplified NAD+ elevation; not inherently harmful but unpredictable in context of inflammatory or oncologic disease | Low-Moderate | No human DDI studies; disclose combination in clinical notes | | NMN | Metformin | Metformin activates AMPK and independently modulates NAMPT expression; additive AMPK signaling may over-suppress mTORC1 | Theoretical over-suppression of mTOR; not observed in current human data | Low | No action required currently; monitor for unexpected fatigue or GI effects | | Tryptophan | MAOIs (phenelzine, tranylcypromine) | MAOIs block MAO-A/B, reducing tryptophan catabolism through the kynurenine arm; serotonin accumulation from tryptophan precursor loading | Serotonin syndrome risk | Severe / Contraindicated | Do not combine tryptophan supplementation with any MAOI; washout 14 days after MAOI discontinuation (11) | | Tryptophan | SSRIs / SNRIs | Additive serotonergic effect via increased serotonin synthesis from tryptophan precursor loading | Serotonin syndrome; milder than MAOI combination but real | Moderate-Severe | Avoid tryptophan doses >1 g/day in patients on SSRIs/SNRIs; if used, start at 500 mg and titrate slowly with symptom monitoring | | Tryptophan | IDO inhibitors (epacadostat, BMS-986205) | IDO inhibition blocks the kynurenine pathway, shunting tryptophan toward serotonin and other routes; unpredictable NAD+ precursor flux | Altered tryptophan catabolism; immune and metabolic off-target effects | Moderate | Monitor kynurenine/tryptophan ratio; avoid unsupervised tryptophan supplementation during IDO inhibitor trials |

Niacin (Nicotinic Acid): The Highest-Risk Precursor for DDIs

Prescription extended-release niacin (Niaspan, 500 mg to 2,000 mg/day) remains the only FDA-approved NAD precursor for a metabolic indication: raising HDL-C and lowering triglycerides in dyslipidemia. Its GPR109A agonism and broad hepatic metabolic footprint give it the most clinically documented DDI profile of any precursor in this class.

Statin Combination: FDA Black-Box Context

The FDA issued a safety communication in 2016 restricting simvastatin doses above 20 mg when combined with niacin >1 g/day, specifically because of rhabdomyolysis cases documented in the AIM-HIGH trial (N=3,414) and post-marketing reports. The AIM-HIGH investigators reported no cardiovascular benefit from adding niacin to statin therapy in patients with established cardiovascular disease and well-controlled LDL-C, while myopathy events were numerically higher in the niacin arm (12). Rosuvastatin and pravastatin carry lower myopathy risk in combination with niacin because they are not CYP3A4 substrates.

Glycemic Effects and Antidiabetic Dose Adjustment

Niacin raises fasting glucose by 5-16 mg/dL and HbA1c by 0.1-0.3% at doses of 1,500-2,000 mg/day through suppression of adipose free fatty acid release and downstream insulin resistance. The ADVENT trial (N=148) showed that extended-release niacin raised fasting glucose a mean 8.7 mg/dL at week 16 in patients with metabolic syndrome (7). Patients on sulfonylureas or insulin may need dose increases of 10-20% to maintain glycemic targets during niacin titration.

Anticoagulation Monitoring Protocol

At niacin doses above 1.5 g/day, INR may rise within 3-7 days. The proposed mechanism involves niacin-induced reduction in fibrinogen and possibly interference with hepatic vitamin K-dependent carboxylation at high hepatic NAD+ flux. Check INR at baseline, at day 7 after reaching 1,500 mg/day, and monthly thereafter. Warfarin dose reductions of 10-15% are often sufficient (6).

NAM (Nicotinamide): PARP and Epigenetic DDIs

Nicotinamide at doses above 500 mg/day is a direct feedback inhibitor of SIRT1 and SIRT3 and a substrate competitor at PARP1/2. These molecular targets are also the targets of growing oncologic and cardiometabolic drug pipelines, creating pharmacodynamic DDI risks that have no precedent in older DDI databases.

PARP Inhibitor Co-Prescription Warning

PARP inhibitors (olaparib 300 mg BID, niraparib 300 mg/day, rucaparib 600 mg BID) achieve antitumor efficacy by trapping PARP on DNA breaks, depleting tumor-cell NAD+ and inducing apoptosis. Pre-clinical data from Tummala et al. Showed that raising intracellular NAD+ via nicotinamide supplementation partially rescued ovarian cancer cell lines from olaparib-induced apoptosis in a dose-dependent manner (8). No prospective human trial has yet measured clinical cancer outcomes during concurrent NAM + PARP inhibitor use, so the conservative position is to withhold high-dose NAM during active PARP inhibitor therapy.

Anticonvulsant Monitoring

At pharmacologic doses used in pellagra treatment (3,000 mg/day) and in some longevity protocols (1,000-2,000 mg/day), NAM inhibits CYP2C19 sufficiently to raise carbamazepine plasma levels by an estimated 20-40%. A 1996 case series by Bourgeois et al. In pediatric epilepsy patients documented toxicity when high-dose NAM was added without drug level adjustment (9). Prescribers adding NAM to any regimen containing carbamazepine, primidone, or phenytoin should check drug levels at 2 weeks.

NR (Nicotinamide Riboside): Emerging Interaction Signals

NR is the most studied next-generation NAD precursor in randomized human trials. Elhassan et al. (2019, N=12 older adults) showed NR 1,000 mg/day for 21 days raised skeletal muscle NAD+ by 30% without significant adverse effects (13). Dollerup et al. (2018, N=40) found NR 2,000 mg/day over 12 weeks produced no significant change in insulin sensitivity in obese men, suggesting limited metabolic DDI risk at standard doses (14).

Chemotherapy Interaction: The DNA Repair Problem

The same NAD+-PARP axis that creates a DDI concern with NAM applies to NR. Pre-clinical models show that raising NAD+ before platinum-based chemotherapy can reduce cisplatin-induced apoptosis in tumor cells by giving PARP more substrate for DNA strand-break repair. Clinically, this has not been tested in an RCT. Until it is, the responsible position is to pause NR supplementation during active chemotherapy cycles and restart 2-3 weeks after the last cytotoxic dose, in coordination with the treating oncologist.

Statin Interaction Nuance

NR is metabolized primarily to NAM in the gut before absorption. Any theoretical statin interaction is therefore mediated through NAM's molecular biology, not NR's. CK monitoring is appropriate for patients taking NR alongside high-intensity statins (rosuvastatin 40 mg, atorvastatin 80 mg), though no published human case series documents myopathy from this combination (13).

NMN (Nicotinamide Mononucleotide): Early Human Data and Interaction Gaps

NMN bypasses the NAMPT rate-limiting step. Yoshino et al. (2021, N=25 postmenopausal women with prediabetes) showed NMN 250 mg/day for 10 weeks improved skeletal muscle insulin sensitivity and upregulated genes involved in muscle remodeling, with no significant adverse events or lab abnormalities (5). A second trial by Yi et al. (2023, N=80) tested NMN 300 or 600 mg/day for 60 days in middle-aged and older adults and reported no significant changes in LFTs, renal function, or hematologic parameters (15).

Metformin Interaction: Mechanistic Overlap

Both NMN and metformin activate AMPK. Metformin does so by inhibiting mitochondrial complex I, raising the AMP:ATP ratio. NMN does so indirectly through SIRT1-mediated LKB1 activation. The combined AMPK stimulation is additive in rodent models, but no human pharmacodynamic DDI study exists (5). Monitor for hypoglycemia in the first 4 weeks of combination use in patients with insulin resistance.

CD38 Inhibitor Combination

Flavonoids apigenin and quercetin inhibit CD38, the dominant NAD+-consuming ecto-enzyme. Co-administration with NMN theoretically amplifies NAD+ elevation by simultaneously increasing synthesis and decreasing catabolism. This combination is increasingly popular in longevity protocols. No controlled human data yet quantifies how large the NAD+ increase is or whether it causes off-target effects in CD38-expressing immune cells (16).

Tryptophan as an NAD Precursor: Serotonergic DDI Dominates

Dietary and supplemental tryptophan is primarily discussed in serotonin pharmacology, but the kynurenine pathway diverts roughly 90-95% of absorbed tryptophan away from serotonin synthesis toward NAD+ production via quinolinic acid. Supplemental tryptophan doses used in sleep and mood protocols (500 mg to 3,000 mg/day) can meaningfully shift NAD+ precursor flux in IDO-competent individuals (17).

Serotonin Syndrome Risk Is Dose-Dependent

The MAOI + tryptophan combination is contraindicated, full stop. Serotonin syndrome cases were documented as early as 1984 when tryptophan was combined with phenelzine. The combination of irreversible MAO-A inhibition with tryptophan precursor loading produces serotonin accumulation that can be fatal. A 2-week washout after MAOI discontinuation before starting tryptophan is the minimum safe interval; 4 weeks is preferred for phenelzine given its irreversible binding (11).

SSRI/tryptophan combinations carry moderate risk. Tryptophan 1 g/day added to fluoxetine 20 mg/day produced serotonin syndrome symptoms (shivering, myoclonus, hyperreflexia) in 4 of 6 subjects in a 1991 crossover study by Steiner and Fontaine (18). Start tryptophan at 500 mg/day maximum in any patient already on serotonergic therapy.

Prescribing Considerations: Monitoring Framework

Prescribers managing patients on NAD precursors should document baseline and follow-up labs based on which precursor and dose is being used.

Baseline Labs by Precursor

| Precursor | Baseline | Follow-up Interval | |---|---|---| | Niacin >500 mg/day | Fasting lipids, LFTs (AST/ALT), fasting glucose, HbA1c, uric acid, INR (if on warfarin) | Every 3 months for 12 months, then every 6 months | | NAM >500 mg/day | LFTs, renal panel; check any narrow-TI drug levels (carbamazepine, phenytoin) | 2 weeks after dose start or change, then every 6 months | | NR or NMN >500 mg/day | LFTs, CK (if statin co-prescription), fasting glucose | 3 months, then annually | | Tryptophan >1 g/day | Baseline serotonin syndrome screen; inquire re: all serotonergic medications | Monthly for 3 months |

The 2018 ACC/AHA Cholesterol Guideline explicitly states: "The addition of niacin to statin therapy does not provide incremental cardiovascular benefit above statin therapy alone and may increase the risk of adverse effects." (19). This should anchor prescriber decision-making before initiating niacin for lipid indications.

Oncology Patients: A Default Pause Protocol

Any patient starting cytotoxic chemotherapy, PARP inhibitor therapy, or IDO inhibitor therapy as part of a clinical trial should pause all NAD precursor supplementation. The mechanism is clear, the downside risk is non-trivial, and no randomized controlled trial has established that continuing NAD precursors during chemotherapy is safe or beneficial in humans. Restart should require oncologist sign-off.

Adverse Effect Profiles by Precursor

Understanding adverse effects helps differentiate drug-related toxicity from DDI-related toxicity in clinical practice.

| Precursor | Common AEs | Serious AEs | Distinguishing Feature | |---|---|---|---| | Niacin | Flushing (73-92% at >500 mg), pruritus, GI upset | Hepatotoxicity (SR formulations), gout, hyperglycemia | Flushing blunted by aspirin 325 mg pre-dose | | NAM | GI nausea at >3 g/day | Reversible hepatotoxicity at >3 g/day | No flushing; no lipid benefit | | NR | Mild GI; nausea at >2,000 mg/day | None documented in RCTs to date | No flushing | | NMN | Mild GI at >600 mg/day | None documented in RCTs to date | No flushing | | Tryptophan | Drowsiness, nausea | Serotonin syndrome (with serotonergic co-meds) | Eosinophilia-myalgia syndrome (historical, contaminated batches) |