- Upset stomach is the most commonly reported side effect, alongside occasional diarrhea or constipation[1]
- Fatigue and drowsiness are frequently mentioned, particularly when starting the supplement[2]
- Skin reactions (itching, redness, mild rashes) are a less common but documented complaint[2]
- A real user complaint centers on value: PEA can be expensive relative to its perceived effectiveness for some pain-management users[3]
PEA (palmitoylethanolamide) is marketed as a gentle, non-cannabinoid option for pain and inflammation support. Research consistently describes it as well-tolerated, and the complaint pattern reflects that, mild and infrequent rather than severe.
Gastrointestinal Discomfort
The most common side effect of PEA is an upset stomach. A small number of people in studies report mild gastrointestinal discomfort such as diarrhea or constipation, with others noting nausea or bloating[1].
Fatigue and Drowsiness
Fatigue and drowsiness are occasionally mentioned in user reports, particularly when first starting the supplement[2], but they are not among the side effects named in the trial reviews, which list mild gastrointestinal discomfort and dizziness [8].
Research note: A double-blind placebo-controlled pilot trial of PEA in people with established chemotherapy-induced neuropathy found PEA failed to improve it [11].
Headaches
Some individuals report headaches, especially when beginning PEA or increasing the dose. If headaches persist, discontinuing use and seeking medical advice is the standard recommendation[2].
Skin Reactions
A less common but documented complaint involves skin reactions, itching, redness, and mild rashes, in some users. Allergic skin reactions are described as relatively rare[2].
A Real User Complaint: Cost vs. Effectiveness
From actual user reviews, one specific and useful complaint stands out: a user reported PEA helps as part of a multi-faceted pain approach, but causes a bit of brain fog/fatigue, and is “very expensive versus low dose Tapentadol and not as effective.” Another user reported that physical activity increased their pain, requiring several days of rest to return to a tolerable level[3]. These are honest effectiveness-vs-cost tradeoffs worth factoring in, separate from any biological side effect.
Trial results on effectiveness are mixed too. In 111 adults with knee osteoarthritis, total WOMAC score fell significantly versus placebo at both 300 mg and 600 mg a day over 8 weeks, but in a separate 12-week knee osteoarthritis trial the primary endpoint was missed and placebo improved more at 4 weeks. In 61 people with carpal tunnel syndrome, PEA 600 mg/day did not improve clinical or electrophysiological measures against placebo [5][9][10].
Rare Effects
Slight nausea, drowsiness, or palpitations have occasionally been mentioned after taking PEA[2], but no verified trial data show how often, so they should not be described as a measured fraction of users.
Long-Term Use Is Understudied
While PEA is generally considered safe for short-term use, the effects of long-term supplementation haven’t been extensively studied, so caution is advised for anyone using it over a prolonged period[2]. It’s also worth noting the FDA hasn’t reviewed PEA for safety and effectiveness.
The Reassuring Baseline
Despite these complaints, the trial record points to serious adverse effects being uncommon. A critical review of the published pain trials concluded that, for treatment up to 49 days, the data argue against serious adverse reactions occurring in 1 in 200 people or more, while noting that too few people have taken PEA for longer than 60 days to say the same for long-term use[4].
What Controlled Trials Actually Recorded
User reviews and side-effect roundups are useful for knowing what people notice, but they cannot tell you how often a complaint happens or whether PEA caused it. A tired afternoon or an upset stomach in the first week of a new supplement can have many causes, and nobody writing a review has a placebo group to compare against. Controlled trials do, so it is worth setting the complaints above against what those trials logged.
The most careful look at the question is a 2016 review in the British Journal of Clinical Pharmacology, which went through sixteen clinical trials, several case reports and pilot studies, and a meta-analysis specifically to test the claim that PEA is free of unwanted effects[4]. Its answer is narrower than marketing copy usually allows. For courses of up to about seven weeks, serious problems look uncommon. Beyond about two months, the data simply run thin, which is the gap the long-term section above refers to. The same review also flagged uneven trial quality, including results reported without any measure of spread.
Individual trials fit that picture. In an 8-week double-blind study of 111 adults with knee osteoarthritis, participants took 300 mg or 600 mg of PEA a day, split into two doses, or a placebo. The authors report no changes in the clinical markers they tracked and describe the product as well tolerated[5]. A 2026 systematic review of PEA for diabetic nerve pain, covering three studies and 188 patients, found the safety reporting limited but confined to mild adverse events that resolved on their own[6]. That review raises its own caveat: several of the studies used PEA inside combination products, which makes it harder to pin any effect, good or bad, on PEA alone.
For the skin complaints, the controlled data that exist concern creams rather than capsules. Patch testing of two commercial topical formulations containing PEA and cannabidiol on healthy volunteers showed no irritation or sensitization[7]. Those products came from a single manufacturer and were tested only on healthy skin, so this does not rule out a rash from an oral supplement. It is, however, a reason not to assume PEA itself is a common skin irritant.
The practical reading for anyone weighing these reviews: a complaint that keeps appearing is worth noticing, but most published trials lasted weeks rather than months and enrolled people with one specific condition. If a reaction persists, or you plan to take PEA for many months, you are in the situation the research covers least, and talking it through with your doctor is the sensible step.
FAQ
What’s the most common PEA side effect?
Upset stomach, along with occasional diarrhea or constipation[1].
Does PEA cause fatigue?
Some users report fatigue or drowsiness, particularly when starting the supplement[2].
Is PEA worth the cost for pain relief?
Real user reviews are mixed: some find it helpful as part of a broader approach, while others find it expensive relative to its effectiveness[3].
References
- WebMD. Palmitoylethanolamide: Overview, Uses, Side Effects, Precautions, Interactions, Dosing and Reviews. www.webmd.com/vitamins-supplements/palmitoyle…
- Neuro-Blast. Palmitoylethanolamide Side Effects: What to Know. neuro-blast.com/palmitoylethanolamide-side-ef…
- WebMD Reviews. Palmitoylethanolamide (PEA) Reviews and User Ratings. reviews.webmd.com/vitamins-supplements/ingred…
- Palmitoylethanolamide for the treatment of pain: pharmacokinetics, safety and efficacy. British Journal of Clinical Pharmacology (2016). PMID 27220803
- A double-blind randomized placebo controlled study assessing safety, tolerability and efficacy of palmitoylethanolamide for symptoms of knee osteoarthritis. Inflammopharmacology (2019). PMID 30927159
- Efficacy, safety, and tolerability of palmitoylethanolamide in the management of diabetic neuropathic pain: a systematic review and meta-analysis. Journal of Diabetes and Metabolic Disorders (2026). PMID 41664677
- Tolerability profile of topical cannabidiol and palmitoylethanolamide: a compilation of single-centre randomized evaluator-blinded clinical and in vitro studies in normal skin. Clinical and Experimental Dermatology (2021). PMID 34022073
- Wang Y et al. Palmitoylethanolamide in the Treatment of Pain and Its Clinical Application Prospects. Drug design, development and therapy (2025). PMID 40827226
- Srivastava S et al. Temporal effects of Palmitoylethanolamide (PEA) in modulating knee osteoarthritis symptoms: A randomized, double-blind, placebo-controlled trial. Journal of back and musculoskeletal rehabilitation (2026). PMID 42635976
- Faig-Martà J et al. Use of palmitoylethanolamide in carpal tunnel syndrome: a prospective randomized study. Journal of orthopaedics and traumatology : official journal of the Italian Society of Orthopaedics and Traumatology (2017). PMID 28299455
- Mellar P. Davis et al. Treatment of Established Chemotherapy-Induced Neuropathy with N-Palmitoylethanolamide: A Randomized, Double-Blind Phase II Pilot Study. Cancers (2024). PMID 39766143
These statements have not been evaluated by the Food and Drug Administration. This information is not intended to diagnose, treat, cure, or prevent any disease. Content is for informational purposes only and is not medical advice; consult a qualified healthcare provider before starting any supplement. As an Amazon Associate we earn from qualifying purchases.