LDN Primer Follow-Up: What to Do When LDN Causes Side Effects

A companion piece to the LDN Primer book, exploring how side effects are actually managed in clinical practice.

LDN Primer Link:

One of the questions I hear most often from readers of my LDN Primer book — and from clients starting low dose naltrexone (LDN) for the first time — isn't "does LDN work?" It's this one:

"I had side effects and had to stop. Now what?"

This is one of the most common forks in the road in LDN care, and it's worth walking through carefully, because the answer is never one-size-fits-all.

First, the side effects themselves aren't usually the problem

LDN is, overall, a well-tolerated medication. Across studies and clinical case series, the most frequently reported issues are vivid or unusual dreams, transient insomnia (especially with evening dosing), mild gastrointestinal upset, and headache. These effects are typically mild, tend to cluster around the start of treatment or a dose increase, and often resolve within one to two weeks even without any change in dose.

But "usually mild" doesn't mean "always mild for everyone." A meaningful minority of clients are simply more sensitive to naltrexone's effects on sleep, mood, or energy — sometimes because of genetics, sometimes because of an underlying condition like MCAS, POTS, or hEDS that already predisposes the nervous system to overreact to new inputs. For these clients, even the traditional "start low and go slow" titration (often beginning around 0.5–1.5 mg and increasing gradually toward a 3–4.5 mg target) can trigger disruptive symptoms.

The instinct to "push through" isn't always the right one

There's a common assumption — sometimes from clients, sometimes from well-meaning online communities — that side effects are just something to tough out until the body adjusts. Sometimes that's true. But in my practice, when side effects are significant enough to interfere with sleep, function, or quality of life, my first recommendation is usually straightforward: stop the LDN.

That's not a failure of the medication or the client. It's simply the safest way to reset and gather information. Once the side effect has cleared and the nervous system has settled, the real clinical work begins: figuring out whether, when, and at what dose to restart.

There is no universal restart dose — and that's the point

This is where LDN care diverges sharply from a "take 4.5 mg and see what happens" approach. The right restart strategy depends entirely on the individual clinical picture: the condition being treated, how sensitive the person's nervous system and opioid-receptor signaling appear to be, what the side effect was, how severe it was, and how the body has responded to other medications and supplements in the past.

For many clients, restarting at a very small microgram dose — a small fraction of the standard milligram-range starting dose — and titrating back up slowly is enough to avoid a repeat of the side effect. For a smaller subset of more sensitive clients, even that isn't gentle enough, and the more appropriate starting point is in the nanogram range. And for a small number of especially reactive individuals, restart may need to begin at the picogram level — an almost vanishingly small amount — before any upward titration is attempted.

To be clear: these ultra-low dosing ranges (microgram, nanogram, and picogram naltrexone) are a distinct and well-described pharmacological concept in the literature, historically studied as an adjunct co-administered with opioid pain medications to enhance analgesia and reduce tolerance, rather than as a standard restart protocol for LDN side effects. Applying this framework to an individualized LDN restart is a matter of clinical judgment — informed by the pharmacology, but tailored case by case — and it's exactly the kind of decision that should be made in partnership with a physician experienced in LDN dosing, not self-directed.

So what do these units actually mean?

If you've never worked with compounded medications before, "microgram," "nanogram," and "picogram" can sound interchangeable — they're all "very small," right? In practice, each step down is a thousand-fold difference from the next, and the differences compound quickly:

Put another way: a microgram is one-thousandth of a milligram. A nanogram is one-thousandth of a microgram. A picogram is one-thousandth of a nanogram. Standard LDN doses are measured in milligrams (typically 1–5 mg/day, with 4.5 mg being a common target). Restart doses in the microgram-to-picogram range are dramatically smaller — often thousands to millions of times smaller than the standard dose — which is precisely why they can allow an especially sensitive person to reintroduce naltrexone without retriggering the side effect that caused the original stop.

The pharmacologic rationale for why doses this small can still do anything at all comes down to receptor-level biology. At these ultra-low concentrations, naltrexone isn't acting primarily through the classic opioid receptor blockade that defines its higher-dose use. Instead, research has identified a distinct, extremely high-affinity binding site on a scaffolding protein called filamin A (FLNA), which sits near the mu-opioid receptor and helps regulate how that receptor signals over time. Binding at this site — which occurs at picomolar concentrations — appears to prevent a shift in receptor signaling (from a Gi/o- to a Gs-coupled state) that is otherwise associated with heightened sensitivity, tolerance, and some of the less pleasant downstream effects of opioid receptor activity. This is the same biological seam that ultra-low-dose naltrexone and naloxone research has explored for decades, primarily in the context of enhancing opioid analgesia — and it's part of why "less can sometimes mean a gentler, more tolerable effect" rather than "less means no effect at all."

The clinical bottom line

If you've had to stop LDN because of side effects, that's not the end of the road — but it also isn't something to troubleshoot on your own with trial and error. The right next step depends on:

• What the side effect was and how severe it was
• The underlying condition LDN was being used for
• How sensitive your system has been to other medications or supplements
• How long you were on LDN, and at what dose, before stopping

From there, a restart plan — whether that means a slower titration from the standard starting dose, or a much smaller microgram, nanogram, or even picogram starting point — should be built around your specific picture, ideally with a physician who has experience titrating LDN across this full range.

If you'd like to go deeper into LDN dosing, mechanisms, and troubleshooting, the LDN Primer book is available on Amazon, and additional educational resources are available through the LDN Support Group community.

About Dr. Kim

Yoon Hang Kim, MD, MPH is Board-Certified in Preventive Medicine | Integrative & Functional Medicine Physician, with over 20 years of experience in integrative and functional medicine. He completed a fellowship at the University of Arizona under Dr. Andrew Weil, holds certifications in medical acupuncture and integrative/holistic medicine, and is an Institute for Functional Medicine (IFM) Scholar. Dr. Kim specializes in low dose naltrexone (LDN), autoimmune conditions, chronic pain, integrative oncology, fibromyalgia, chronic fatigue syndrome (CFS), mast cell activation syndrome (MCAS), and mold toxicity/CIRS. He is the author of three books and more than 20 published articles.

Learn more at www.yoonhangkim.com | www.directintegrativecare.com

References

1. Toljan K, Vrooman B. Low-Dose Naltrexone (LDN)—Review of Therapeutic Utilization. Med Sci (Basel). 2018;6(4):82. PMID: 30248938; PMCID: PMC6313374.
2. Raknes G, Småbrekke L, et al. (as reviewed in) The use of low-dose naltrexone (LDN) as a novel anti-inflammatory treatment for chronic pain. PMC, PMCID: PMC3962576.
3. Wang H-Y, Frost EAM, Burns LH. Ultra-Low-Dose Naloxone or Naltrexone to Improve Opioid Analgesia: The History, the Mystery and a Novel Approach. Clin Med Insights Ther. 2010. DOI: 10.4137/CMT.S4870.
4. Burns LH, Wang H-Y. High-Affinity Naloxone Binding to Filamin A Prevents Mu Opioid Receptor–Gs Coupling Underlying Opioid Tolerance and Dependence. PLoS ONE / PMC, PMCID: PMC2212716.
5. McKenzie-Brown AM, Boorman DW, Ibanez KR, Agwu E, Singh V. Low-Dose Naltrexone (LDN) for Chronic Pain at a Single Institution: A Case Series. J Pain Res. 2023;16:1993-1998. PMID: 37337611; PMCID: PMC10276990.

This article is for educational purposes and does not constitute individualized medical advice. Any decision to stop, restart, or adjust LDN dosing should be made in consultation with a physician familiar with your full clinical history.