Kratom and Thyroid: One Case Report, Multiple Contradictions

The discrepancy is stark: one 44-year-old man developed hypothyroidism after four months of using internet-purchased kratom of unknown purity, while systematic studies of long-term traditional users found completely normal thyroid parameters. The case report authors themselves acknowledged this was an observed "coincidence" rather than proven causation and called for experimental investigation—investigation that subsequent observational studies failed to corroborate.

The single case claiming thyroid dysfunction

The only peer-reviewed study suggesting a kratom-thyroid link is Sheleg SV, Collins GB. "A coincidence of addiction to 'Kratom' and severe primary hypothyroidism." Journal of Addiction Medicine. 2011 Dec;5(4):300-301. DOI: 10.1097/ADM.0b013e318221fbfa. PMID: 21817918.

This is a case report—the lowest tier of medical evidence—describing one patient who developed severe primary hypothyroidism concurrent with kratom use. The 44-year-old male had a history of alcohol use disorder and used his wife's Percocet before switching to kratom purchased from an internet vendor. After approximately four months, he experienced 60-pound weight gain, lethargy, and a myxedematous face. Blood tests confirmed elevated TSH indicating primary hypothyroidism. He was treated with levothyroxine for thyroid dysfunction and buprenorphine for opioid withdrawal.

The authors speculated that "high dose of indole alkaloid mitragynine (the major alkaloid identified from Kratom) might reduce the normal response of the thyroid gland to thyroid-stimulating hormone resulting in primary hypothyroidism." They explicitly called for "further experimental investigations of mitragynine as a possible suppressor of thyroid gland function."

Funding: According to subsequent literature citing this work, the study received partial support from NIH grants AR053483 and GM104938—federal government funding with no pharmaceutical or kratom industry involvement.

Conflicts of interest: The authors declared no potential conflicts of interest.

Independent verification: None. This finding has never been replicated in the 14 years since publication, despite multiple subsequent studies specifically monitoring thyroid function in kratom users.

Critical limitations: The study design cannot establish causation—only temporal association. The title itself uses "coincidence," acknowledging this limitation. The patient had significant confounding factors including alcohol use disorder and concurrent medication use. No baseline thyroid measurements existed before kratom use, the product's composition and purity were unknown, and alternative causes of hypothyroidism were not ruled out. Single case reports represent the weakest form of medical evidence.

Multiple studies finding no thyroid effects

Four peer-reviewed studies by Singh and colleagues systematically examined thyroid function in kratom users and found no evidence of dysfunction.

Study 1: Malaysian Cross-Sectional Study (2018)

Singh D, Müller CP, Murugaiyah V, et al. "Evaluating the hematological and clinical-chemistry parameters of kratom (Mitragyna speciosa) users in Malaysia." Journal of Ethnopharmacology. 2018 Mar 25;214:197-206. DOI: 10.1016/j.jep.2017.12.017. PMID: 29248450.

This cross-sectional study compared 58 regular kratom users to 19 healthy controls, conducting comprehensive blood tests including thyroid screening. The study found no significant differences in thyroid function between groups. The authors concluded that "even long-term and heavy kratom consumption did not significantly alter the hematological and clinical-chemistry parameters" including thyroid analytes. This study used GC-MS laboratory analysis to verify mitragynine content in kratom samples, ensuring standardized measurements.

Study type: Cross-sectional comparative study. Funding: Conducted at Centre for Drug Research, Universiti Sains Malaysia (government-affiliated institution). Conflicts of interest: Not disclosed. Independent verification: This directly contradicts the Sheleg & Collins case report by demonstrating normal thyroid function in a cohort of regular users.

Study 2: Long-Term Users Study (2020)

Singh D, Narayanan S, Grundmann O, et al. "Long-Term Effects of Kratom (Mitragyna speciosa) Use." Malaysian Journal of Medicine and Health Sciences. 2020 Dec;16(4):64-72.

This cross-sectional pilot study examined 13 regular kratom users with more than 20 years of continuous use—far exceeding the four-month exposure in the case report. Mean duration of use was 20.4 years, with daily mitragynine intake averaging 87.54 mg. The study explicitly stated: "There were no alterations in the thyroid function...of the respondents. It appears that regular kratom consumption in the form of a decoction did not impair their thyroid function." Thyroxine (T4) levels averaged 111.4 nmol/L (SD=29.8), well within the normal reference range of 64.0-167.0 nmol/L. Even comparing high consumption users (>3 glasses daily) to low consumption users showed no significant thyroid differences (p=0.093).

Study type: Cross-sectional study of very long-term users. Funding: Ministry of Higher Education Malaysia under the Higher Institution Centres of Excellence (HICoE) grant—government funding with no commercial ties. Conflicts of interest: Authors declared none. Independent verification: Provides the strongest contradictory evidence, as users had >20 years exposure versus the 4-month exposure in the case report.

Study 3: Longitudinal Follow-Up Study (2021)

Singh D, Narayanan S, Grundmann O, et al. "Comparison of biochemical and safety parameters of regular kratom (Mitragyna speciosa Korth.) users at two different time periods." Journal of Substance Use. 2021;28(1). DOI: 10.1080/14659891.2021.1999513.

This prospective longitudinal study followed 5 male regular kratom users over three months with repeated blood tests at baseline and follow-up. Daily mitragynine doses ranged from 76.3-114.8 mg. The study found that "kidney, liver function tests, thyroid, and glucose parameters were not significantly affected." The authors concluded that "continuous consumption of kratom decoction...did not appear to alter the safety hematological and biochemical parameters of kratom users."

Study type: Longitudinal study with repeated measures. Funding: Not explicitly stated in available abstracts. Conflicts of interest: Not stated. Independent verification: Provides prospective evidence that continued kratom use over time does not lead to thyroid dysfunction.

Study 4: Endocrine Function Study (2018)

Singh D, Murugaiyah V, Hamid SBS, et al. "Assessment of gonadotropins and testosterone hormone levels in regular Mitragyna speciosa (Korth.) users." Journal of Ethnopharmacology. 2018 Jul 15;221:30-36. DOI: 10.1016/j.jep.2018.04.005. PMID: 29626673.

This cross-sectional endocrine study examined 19 regular kratom users with more than 2 years of use (daily mitragynine dose 76.23-94.15 mg). While focused on testosterone and gonadotropins, the study also monitored thyroid hormones and found no impairment of tetraiodothyronine (T4) levels. The authors stated: "We found long-term kratom tea/juice consumption...did not impair testosterone levels, or gonadotrophins, hematological and biochemical parameters."

Study type: Cross-sectional endocrine study. Funding: Centre for Drug Research, Universiti Sains Malaysia. Conflicts of interest: Not stated. Independent verification: Specifically tested thyroid hormone (T4) and found no dysfunction, contradicting the hypothyroidism case report.

Expert reviews reach consistent conclusions

Frontiers in Psychiatry Review (2017)

Fluyau D, Revadigar N. "Biochemical Benefits, Diagnosis, and Clinical Risks Evaluation of Kratom." Frontiers in Psychiatry. 2017 Jun 7;8:62. DOI: 10.3389/fpsyt.2017.00062. PMID: 28642715.

This systematic review explicitly stated: "There has been no suggested evidence on both animal or human studies of the effect of kratom on the thyroid gland." The authors declared no commercial or financial conflicts of interest and noted that aside from the single Sheleg & Collins case report, no experimental evidence links kratom to thyroid dysfunction.

Current Emergency Medicine Review (2019)

Alsarraf E, Myers J, Culbreth S, Fanikos J. "Kratom from Head to Toe—Case Reviews of Adverse Events and Toxicities." Current Emergency and Hospital Medicine Reports. 2019;7:141-168. DOI: 10.1007/s40138-019-00194-1.

This comprehensive review examined kratom adverse event reports including endocrine effects. While citing the Sheleg & Collins case, the review noted that "a cross-sectional study of 19 long-term kratom consumers (76 to 94 mg of MG per day for more than 2 years) neither found the substance impairing to the levels of tetraiodothyronine, testosterone, or gonadotrophins nor did it show a dose-dependent effect of kratom on these hormones."

Notably, another case report discussed in this review (LaBryer et al. 2018) involving kratom-induced hyperprolactinemia found normal TSH levels, further suggesting kratom does not typically affect thyroid function.

Why the evidence points away from causation

The preponderance of evidence strongly suggests kratom does not cause thyroid dysfunction. The single case report has multiple weaknesses: uncontrolled conditions, unknown product purity from an internet vendor, confounding factors (alcohol use disorder, concurrent medications), absence of baseline thyroid measurements, and inability to rule out alternative causes. Most critically, it remains an isolated observation never replicated despite opportunities to do so.

In contrast, studies finding no effect employed larger sample sizes (5 to 77 participants versus 1), longer exposure durations (up to 20+ years versus 4 months), controlled study designs with comparison groups, standardized product preparation (traditional decoctions with verified mitragynine content), and systematic thyroid function testing. All received government funding without commercial conflicts of interest.

The methodological hierarchy strongly favors the null findings. Cross-sectional studies with controls, longitudinal studies with repeated measures, and systematic biochemical analyses represent substantially stronger evidence than a single uncontrolled case report. The fact that the longest-duration study found completely normal thyroid function after decades of daily use directly contradicts a case suggesting dysfunction after months.

Conclusion: No established link, but limited research

Current peer-reviewed medical evidence does not support a causal link between kratom use and thyroid dysfunction. Only one case report from 2011 observed hypothyroidism coinciding with kratom use, but this association has not been replicated in any subsequent research. Four controlled studies specifically monitoring thyroid function—including users with over 20 years of daily exposure—found no evidence of thyroid impairment. Systematic reviews conclude there is no experimental evidence linking kratom to thyroid effects.

The scientific consensus based on available evidence is that kratom does not significantly alter thyroid function. However, this conclusion rests on observational studies rather than randomized controlled trials. The original case report authors' call for "further experimental investigations" remains unanswered by rigorous mechanistic studies. While current evidence suggests no thyroid risk, the limited number of studies and lack of large-scale clinical trials means this question has not been exhaustively investigated. The existing evidence base, though consistent in finding no effect, would benefit from larger prospective studies and controlled experimental research to definitively resolve this question.

Complete Reference List

1. Sheleg SV, Collins GB. "A coincidence of addiction to 'Kratom' and severe primary hypothyroidism." Journal of Addiction Medicine. 2011;5(4):300-301. https://pubmed.ncbi.nlm.nih.gov/21817918/
2. Singh D, Müller CP, Murugaiyah V, et al. "Evaluating the hematological and clinical-chemistry parameters of kratom (Mitragyna speciosa) users in Malaysia." Journal of Ethnopharmacology. 2018;214:197-206. https://pubmed.ncbi.nlm.nih.gov/29248450/
3. Singh D, Narayanan S, Grundmann O, et al. "Long-Term Effects of Kratom (Mitragyna speciosa) Use." Malaysian Journal of Medicine and Health Sciences. 2020;16(4):64-72. https://medic.upm.edu.my/upload/dokumen/2020120208295609_MJMHS_0697.pdf
4. Singh D, Narayanan S, Grundmann O, et al. "Comparison of biochemical and safety parameters of regular kratom (Mitragyna speciosa Korth.) users at two different time periods." Journal of Substance Use. 2021;28(1). https://www.tandfonline.com/doi/full/10.1080/14659891.2021.1999513
5. Singh D, Murugaiyah V, Hamid SBS, et al. "Assessment of gonadotropins and testosterone hormone levels in regular Mitragyna speciosa (Korth.) users." Journal of Ethnopharmacology. 2018;221:30-36. https://pubmed.ncbi.nlm.nih.gov/29626673/

6. Fluyau D, Revadigar N. "Biochemical Benefits, Diagnosis, and Clinical Risks Evaluation of Kratom." Frontiers in Psychiatry. 2017;8:62. https://www.frontiersin.org/journals/psychiatry/articles/10.3389/fpsyt.2017.00062/full
7. Alsarraf E, Myers J, Culbreth S, Fanikos J. "Kratom from Head to Toe—Case Reviews of Adverse Events and Toxicities." Current Emergency and Hospital Medicine Reports. 2019;7:141-168. https://link.springer.com/article/10.1007/s40138-019-00194-1