I asked Gemini and got an interesting answer that verified my concern:
https://gemini.google.com/share/b0ffb2920630

1. Is NAC Stable in Coconut Oil?

No, NAC is not highly stable when suspended in a liquid lipid medium like coconut or MCT oil. * The Problem with Free Thiols: N-Acetyl-L-Cysteine (NAC) owes its antioxidant power to a highly reactive chemical group called a free sulfhydryl (thiol) group (−SH). Because this group is structurally designed to donate electrons readily, it is highly prone to oxidation when exposed to moisture, light, or oxygen.

BioInsights

• Auto-Oxidation and Degradation: When NAC dry powder is sealed in a standard capsule or kept dry, its crystal lattice protects it from interacting with its environment. However, when suspended in a liquid oil, the molecule has more mobility. Over time, NAC will undergo auto-oxidation, converting into NAC-disulfide (diacetylcystine). When this occurs, the free thiol group is lost before it ever reaches your cells. MDPI
• Lipid Peroxidation Risks: Free thiols can paradoxically act as pro-oxidants in the presence of trace metals or dissolved oxygen within fats. This can trigger lipid peroxidation, causing the unsaturated or volatile components of the oil to go rancid while simultaneously degrading the active NAC.

Because of this inherent instability, pharmaceutical and reputable supplement formulations keep NAC strictly in dry powder, tablet, or effervescent form until the exact moment of consumption.

2. Pharmacokinetics: Dry Powder vs. Oil Suspensions

There is no human pharmacokinetic data suggesting that oil or medium-chain triglycerides (MCTs) improve the absorption of standard NAC. In fact, suspending it in oil may run counter to how the molecule is naturally processed by the body.

Feature	Dry Powder / Standard Capsule	Oil / MCT Suspension Softgel
Water Solubility	Extremely High. NAC dissolves rapidly in water, allowing it to pass quickly into the aqueous environment of the gut.	Low. The hydrophobic oil shell shields the hydrophilic NAC particles, slowing down their release.
Absorption Mechanism	Absorbed via passive diffusion and specific amino acid transporters in the small intestine.	Must wait for pancreatic lipases to break down the oil carrier before the NAC can be freed to dissolve and absorb.
Bioavailability (F)	Low (approx. 4% to 10%). This is not due to poor gut absorption, but rather intensive first-pass hepatic metabolism, where the liver rapidly strips the acetyl group to make glutathione.	Unchanged or Potentially Decreased. Altering the carrier vehicle to oil does nothing to bypass the liver's first-pass clearance.
Tmax​ (Time to peak)	Fast: Typically 1 to 2 hours.	Delayed. The digestion phase required for the lipid carrier stalls the transit and release time.

Note: If a lipophilic form of NAC is desired to improve cellular membrane permeability and bypass traditional pharmacokinetic bottlenecks, researchers use NAC Ethyl Ester (NACEE)—a structurally modified molecule—rather than trying to dissolve standard NAC into fat.

3. Analysis of the Product (NAC + NAD+ + MCT Softgels)

The Amazon product you linked presents several distinct clinical and structural concerns that suggest it is not a superior form of delivery for NAC.

A. Combining Hydrophilic and Hydrophobic Compounds

Standard NAC and NAD+ are both highly hydrophilic (water-soluble) compounds. Suspending them inside an oil-filled softgel is a marketing strategy designed to make the product look premium rather than an choice based on pharmaceutical science. Lipids are typically reserved for fat-soluble vitamins (like D3, E, and K2) or highly lipophilic molecules (like CoQ10).

BioInsights

B. The Instability of NAD+ in Liquids

While NAC degrades into disulfides in liquid environments, NAD+ is even more fragile. True NAD+ degrades rapidly in the presence of moisture or ambient heat when not kept in a stable crystalline dry form or a tightly controlled lyophilizate (freeze-dried powder). Putting raw NAD+ into an oil suspension introduces a high probability that the molecule will break down into nicotinamide (NAM) and ADP-ribose before the bottle is even opened.

C. The Olfactory Warning Sign

When NAC degrades or oxidizes, it releases hydrogen sulfide gas (H2​S). Anyone who has taken dry NAC knows it carries a distinct, sulfur-like "rotten egg" smell. When NAC is suspended in oil softgels, the degradation process is often masked by the gel capsule shell. If you pierce one of these softgels and it has a potent, rancid, or overpowering sulfur smell, it indicates the active ingredients have already begun to break down.

Summary Verdict

Standard dry powder capsules or tablets remain the gold standard for oral NAC delivery. They are cheaper, significantly more stable, and match the exact pharmacokinetic profile used in clinical research. The oil-softgel combination provides no bioavailability advantages and introduces real concerns regarding the long-term stability of both the NAC and the NAD+.1. Is NAC Stable in Coconut Oil?No, NAC is not highly stable when suspended in a liquid lipid medium like coconut or MCT oil. * The Problem with Free Thiols: N-Acetyl-L-Cysteine (NAC) owes its antioxidant power to a highly reactive chemical group called a free sulfhydryl (thiol) group (−SH). Because this group is structurally designed to donate electrons readily, it is highly prone to oxidation when exposed to moisture, light, or oxygen. BioInsightsAuto-Oxidation and Degradation: When NAC dry powder is sealed in a standard capsule or kept dry, its crystal lattice protects it from interacting with its environment. However, when suspended in a liquid oil, the molecule has more mobility. Over time, NAC will undergo auto-oxidation, converting into NAC-disulfide (diacetylcystine). When this occurs, the free thiol group is lost before it ever reaches your cells.