Effects of long-term exposure to ramelteon, a melatonin receptor agonist, on endocrine function in adults with chronic insomnia

Effects of long-term exposure to ramelteon, a melatonin receptoragonist, on endocrine function in adults with chronic insomnia

Gary Richardson1* and Sherry Wang-Weigand2

1Henry Ford Hospital, Sleep Disorders and Research Center, Detroit, MI, USA2Takeda Global Research and Development Center, Deerfield, IL, USA

Objective To evaluate the effects of ramelteon, an MT1/MT2 melatonin receptor agonist used to treat insomnia, on endocrine function inadults with chronic insomnia.Methods This was a double-blind, placebo-controlled, trial of adults (18–45 years) with chronic insomnia. Subjects received eitherramelteon 16mg or placebo nightly for 6 months. Hormonal measures of the thyroid, reproductive, and adrenal axes were analyzed monthlyand compared with baseline and placebo values.Results While isolated changes were detected at some time points, there were no consistent statistically significant differences betweentreatments on measures of thyroid function (total T4, free T4, TSH, and total T3), adrenal function (AM cortisol, and ACTH), or on mostreproductive endocrine measures [LH, FSH, estradiol (women), total, and free testosterone (men)]. Prolactin concentrations were increasedoverall in women in the ramelteon group compared with placebo (p¼ 0.003). No clinical effects of elevated prolactin were reported; averagemenstrual cycle length, duration of menses, and ovulation probability did not differ between groups.Conclusions Long-term exposure to ramelteon 16mg, a potent melatonin receptor agonist, resulted in mild, transient increase in prolactin,in women only, that were not associated with measurable reproductive effects. There were no consistent changes in other endocrine measures.Copyright # 2008 John Wiley & Sons, Ltd.

key words—ramelteon; melatonin receptor agonist; insomnia; prolactin

INTRODUCTION

The principal hormonal product of the pineal gland,melatonin, has a prominent role in regulating seasonalchanges in physiology, most notably reproduction(Matthews et al., 1993). In seasonally breedinganimals, melatonin is an essential link between photicsystems that measure sunlight and day length and theendocrine responses that facilitate or inhibit reproduc-tion according to the season (Matthews et al., 1993;Pang et al., 1998). While the precise mechanism ofaction is not known, melatonin is presumed to activatespecific melatonin receptors (MT1 and MT2) present inthe hypothalamus of seasonal breeding species (Panget al., 1998).In humans, the effects of melatonin on reproduction

and related endocrine physiology remain unclear.Melatonin levels have been shown to increase during

pregnancy, suggesting a possible role in human re-production (Kivela, 1991; Tamura et al., 2008). Whilethere is some evidence for intact seasonal modulationof reproduction (Wehr, 2001), the effect appears to besmall. Peripheral effects of melatonin on gonadalfunction have been described (Luboshitzky et al.,2002); however, other data suggest that seasonalchanges in human reproduction are minimal (Macchiand Bruce, 2004). For example, autoradiographicstudies of melatonin receptors in the adult humanbrain showed only sporadic binding in the pars tuber-alis that is thought to mediate the neuroendocrinecorrelates of seasonal breeding in other species(Weaver et al., 1993).Several studies have examined the effects of

exogenous melatonin on hormonal indices in humansubjects of varying ages in both men and women, usingdoses of melatonin ranging from 1.5 to 5mg anddurations of exposure from 1 to 90 days (Bellipanniet al., 2001; Forsling et al., 1999; Kostoglou-Athanassiou et al., 1998; Rajaratnam et al., 2003).Most of the studies were quite small, and the dependent

human psychopharmacologyHum. Psychopharmacol Clin Exp 2009; 24: 103–111.

Published online 17 December 2008 in Wiley InterScience

(www.interscience.wiley.com) DOI: 10.1002/hup.993

*Correspondence to: G. Richardson, Henry Ford Hospital, Sleep Disordersand Research Center, 2799 West Grand Blvd., CFP-3 Detroit, MI 48202,USA. Tel.: 313 916-2600. Fax: 313 916-5167. E-mail: [email protected]

Copyright # 2008 John Wiley & Sons, Ltd.

Received 18 June 2008

Accepted 22 October 2008

measures employed varied from study to study; thus itwas difficult to determine whether there was anyconsistent endocrine response to exogenous melatoninadministration in humans.Ramelteon is a potent MT1/MT2 melatonin receptor

agonist used for the treatment of insomnia. In studies ofup to 1 year in duration, ramelteon has been shown toreduce sleep latency in adults with chronic insomnia(DeMicco et al., 2006; Roth et al., 2006; Roth et al.,2007; Wang-Weigand et al., 2007; Zammit et al.,2007). Receptor binding studies using CHO cellstransfected with human MT1 or MT2 receptors indi-cate that ramelteon has greater affinity for MT1

(Ki¼ 14.0 pM) and MT2 (Ki¼ 112.0 pM) receptorsthan melatonin (Ki¼ 80.7 and 383 pM, respectively)(Kato et al., 2005). Ramelteon is also 3.7 times morepotent than melatonin at the MT1 receptor and 17 timesmore potent at the MT2 receptor, as measured by theinhibition of forskolin-induced cAMP production(Kato et al., 2005). Unlike melatonin, ramelteondemonstrates no appreciable affinity for MT3 bindingsites (1/110 that of melatonin) (Kato et al., 2005). Adistinct melatonin binding site, MT3, is linked to aquinone reductase located in both CNS and peripheraltissue (Nosjean et al., 2001). While the functionalconsequences of melatonin binding atMT3 sites are notknown, animal studies suggest that endocrine effects ofmelatonin are essentially attributable to MT1/MT2

receptor activity. Ramelteon has shown no significantaffinity for other receptors or binding sites, nor does itaffect the activity of a wide variety of enzymes (Katoet al., 2005). For these reasons, ramelteon offers aunique opportunity to evaluate the specific role of MT1

and MT2 melatonin receptors in human endocrinefunction. In addition, for those people taking ramelteonfor the treatment of insomnia, the long-term effects onendocrine functions need to be examined.

MATERIALS AND METHODS

Study population

Subjects eligible for this study met the followingcriteria: a diagnosis of chronic primary insomnia(DSM-IV-TRTM), age 18–45 years, a body mass indexbetween 18 and 34 kg/m2, and serum hormoneconcentrations within the normal range. All studyparticipants were required to have a subjective sleeplatency (sSL) of greater than 45min, and a subjectivetotal sleep time (sTST) of less than 6.5 h for at least 3nights a week, as well as a habitual bedtime between8:30 PM and 12:00AM. Subjects were excluded fromthe study if they had participated in any previous

studies of ramelteon, taken any other investigationaldrug within 30 days, or if they had any significantchanges in their sleep schedule in the 7 days prior toinitial screening. Other exclusion criteria included anycurrent or prior condition that might affect sleep orendocrine function or pose a safety risk. All protocolswere approved by the institutional review board foreach study site, and informed consent was obtained foreach participant. The study was conducted according tothe protocol, applicable Food and Drug Administrationlaws and regulations, the World Medical AssociationDeclaration of Helsinki (1989), and the InternationalConference for Harmonization (ICH) HarmonizedTripartite Guideline for Good Clinical Practice.

Study design

This 6-month, randomized, double-blind, placebo-controlled study was conducted at multiple sites toevaluate the effects of ramelteon 16mg (twice theapproved therapeutic dose) on long-term endocrinefunction. A higher than recommended dose oframelteon was selected for this safety study in orderto maximize the possibility of detecting any significantchanges in endocrine function. Subjects were initiallyscreened during the 3 weeks prior to the start of thestudy for eligibility, based on the inclusion andexclusion criteria. During screening, medical and sleephistories were obtained, vital signs were assessed,clinical laboratory tests were performed, and a 12-leadelectrocardiogram (ECG) was completed. On day 1 oftreatment, patients were randomly assigned to takeramelteon 16mg or placebo nightly for 6 months.Baseline values were obtained for serum total T4, freeT4, TSH, T3, LH, FSH, estradiol (women only), totaltestosterone (men only), free testosterone (men only),prolactin, ACTH, and cortisol. An ACTH stimulationtest, using a cosyntropin challenge, was also per-formed. Concentrations of T4, free T4, TSH, T3, LH,FSH, and prolactin were determined using the AxSYMimmunological assay from Abbott Laboratories(Abbott Park, IL). Estradiol concentrations weredetermined using a radioimmunoassay from Diagnos-tic Products Corporation (Los Angeles, CA). Cortisoland ACTH were measured using the Elecsys immuno-logical assay from Roche Diagnostics (Basel, Switzer-land). Total and free testosterone concentrations weredetermined using HPLC Mass Spectrometry andEquilibrium Dialysis, respectively, from Esoterix Inc(Calabasas Hills, CA). Normal reference ranges forhormonal concentrations were as follows: total T4(54–161 nmol/L), free T4 (9–24 pmol/L), TSH (0.32–5mU/L), T3 (0.69–2.11 nmol/L), LH (2–12 IU/L for

Copyright # 2008 John Wiley & Sons, Ltd. Hum. Psychopharmacol Clin Exp 2009; 24: 103–111.DOI: 10.1002/hup

104 g. richardson and s. wang-weigand

men, 0–105 IU/L for women), FSH (1–15 IU/L formen, 2–138 IU/L for women), estradiol (0–1468 pmol/L), total testosterone (350–1030 ng/dL), free testos-terone (52–280 pg/mL), prolactin (1.61–18.77mg/L formen, 1.39–24.20mg/L for women), cortisol (138–442 nmol/L for men, 166–718 nmol/L for women), andACTH (2–12 pmol/L).Premenopausal women were instructed to maintain a

menstrual diary and were given an LH surge home testkit. Patients returned to the clinic monthly for physicalexaminations, assessment of hormone concentrations,and recording of adverse events (AEs). If at anytime during the study a subject had a cortisol levelbelow normal levels, an ACTH stimulation test wasperformed. At months 3 and 6, a full panel of clinicallaboratory tests and an ECG were also performed.Samples for laboratory tests were collected within 3 hof awakening under fasting conditions. Women werealso tested for possible pregnancy, and menstrualdiaries were evaluated. A 2-week, medication-freewashout period followed the 6-month treatment period.After the washout period, patients returned to theclinic for a final visit, during which final hormoneconcentrations were obtained, physical examswere performed, and AEs and menstrual diaries wereassessed.

Statistical analysis

Statistical analyses were based on observed data only.The primary endpoint for this study was change frombaseline in total serum T4 concentration. A repeatedmeasures analysis was performed over the entire6-month study. Changes from baseline for both theramelteon 16mg and placebo group were comparedusing a full multivariate normal model, with treatment,pooled center, gender, month, subject, and treatment-by-period interaction as factors, with baseline T4 andage as covariates. A pooled center indicates a pre-specified combination of subjects from two or moresmall treatment centers to ensure a balance of treatmentgroups. Comparisons between the ramelteon andplacebo group for each month, as well as comparisonsfrom baseline, were performed using t tests, with leastsquares mean and standard error obtained from ananalysis of covariance (ANCOVA) model. Secondaryendocrine values, including TSH, T3, LH, FSH,estradiol (women only), testosterone (men only),prolactin, and AM cortisol were evaluated using thesame statistical tests. Results of the ACTH challengewere evaluated 30 and 60min post dose (cosyntropin)on day 1 and month 6 using an ANCOVA model with

treatment, pooled center, and gender as factors, withbaseline value and gender as covariates.

RESULTS

A total of 122 subjects (53 men, 69 women), with amean age of 34.3 years, participated in the study. Sixty-six subjects (41 placebo, 25 ramelteon) completed theentire 6-month protocol. Reasons for withdrawalincluded occurrence of an AE (2 placebo, 6 ramelteon),lack of efficacy (5 placebo, 5 ramelteon), protocoldeviation (5 placebo, 5 ramelteon), withdrawal of con-sent (4 placebo, 10 ramelteon), investigator’s discre-tion (2 placebo), pregnancy (1 placebo), borderlinecortisol concentration (1 ramelteon), and lack offollow-up (5 placebo, 5 ramelteon).Results of the overall changes (at all time points)

from baseline in endocrine measures for men andwomen are shown in Tables 1 and 2. None of thethyroid measures (TSH, free T4, total T4, T3) showedany significant overall differences from placebo for the6-month study. Assessments of interim time pointsshowed a small increase in T3 concentration in theramelteon group (both men and women) at month 3that reached statistical significance (p¼ 0.034) com-pared with placebo, but the effect was transient, andno differences were detected at subsequent visits(Figure 1).Measures of reproductive hormones (free testoster-

one [men only], total testosterone [men only], estradiol[women only], LH, FSH) did not reveal any overallsignificant differences from placebo (Tables 1 and 2).Interim analyses did show free testosterone wassignificantly increased from placebo at month 1(p¼ 0.028), but again the effect was transient, andno differences were detected at subsequent visits(Figure 2).No significant alterations in adrenal function

between the two groups were detected using measuresof ACTH and cortisol at any time point. No differencesbetween ramelteon 16mg and placebowere detected inthe ACTH stimulation test at day 1 (before first doseof study drug) or at month 6 (last day of treatmentperiod). Baseline cortisol levels were 366.6 nmol/Lfor the placebo group and 369.2 nmol/L for theramelteon group. On day 1, both the placebo andramelteon groups demonstrated mean increased corti-sol levels over baseline at 30min (272.0 nmol/Lplacebo, 274.2 nmol/L ramelteon, p¼ 0.905) and60min (384.0 nmol/L placebo, 381.6 nmol/L ramel-teon, p¼ 0.910) after cosyntropin administration. Atmonth 6 (or early termination date), both the placeboand ramelteon groups demonstrated mean increased


effects of ramelteon on endocrine function 105

cortisol levels over baseline at 30min (269.6 nmol/Lplacebo, 299.6 nmol/L ramelteon, p¼ 0.307) and60min (358.9 nmol/L placebo, 391.9 nmol/L ramel-teon, p¼ 0.292) after cosyntropin administration.Prolactin concentrations in women were increased

overall in the ramelteon group compared with placebo(p¼ 0.003) (Table 2), with statistically significantincreases detected at month 1 (p¼ 0.004), month 2(p¼ 0.018), and month 4 (p¼ 0.007) (Figure 3). Nosignificant changes in mean prolactin levels weredetected in men overall (p¼ 0.414) or at any specifictime point. Elevated prolactin levels at any time pointduring the treatment phase were detected in 38% ofwomen and 14% of men taking ramelteon, and 11% ofwomen and 27% of men taking placebo. Two subjectsin the ramelteon group discontinued the study due toelevated levels of prolactin (1 man and 1 woman).None of the elevated prolactin levels were associatedwith clinical symptoms.

The overall mean change in prolactin concentrationfor women was small (4.9mg/L), and there was noevidence of reproductive consequences that might beattributed to a prolactin increase. Specifically, therewas no significant difference (p¼ 0.553) in the overallprobability of ovulation (measured by LH surge)during the menstrual cycles of premenopausal womenbetween the placebo and ramelteon groups (60.9 and65.2% of menstrual cycles were associated withpositive ovulation, respectively). The menstrual cyclelength, duration of menstrual flow, and intensity ofbleeding were similar between the two groupsthroughout the study (Table 3).AEs were reported in 85 out of 122 patients (46

placebo, 39 ramelteon), and most were mild ormoderate in intensity. The incidence of reproductivesystem or breast disorder AEs was similar between theramelteon (6 increased prolactin, 3 dysmenorrhea, 2irregular menstruation, 1 amenorrhea) and placebo

Table 1. Summary of the overall changes from baseline for the thyroid, adrenal, and reproductive axes in men

Variable Placebo (n¼ 30) Ramelteon 16mg (n¼ 22) p-value (comparison with placebo)

Thyroid axisTSH (mU/L)Baseline 1.7 (0.13) 1.4 (0.15) 0.820Overall change from baseline 0.2 (0.10) 0.2 (0.11)

Free T4 (pmol/L)Baseline 13.7 (0.32) 12.7 (0.38) 0.154Overall change from baseline �0.1 (0.17) �0.4 (0.20)

Total T4 (nmol/L)Baseline 93.0 (2.56) 87.1 (3.02) 0.865Overall change from baseline 2.1 (1.73) 1.7 (1.96)

T3 (nmol/L)Baseline 1.4 (0.04) 1.5 (0.05) 0.187Overall change from baseline 0.0 (0.03) 0.1 (0.03)

Reproductive axisFree testosterone (pg/mL)Baseline 97.0 (4.70) 102.6 (5.55) 0.052Overall change from baseline �3.7 (5.02) 11.6 (5.68)

Total testosterone (ng/dL)Baseline 428.0 (24.34) 463.1 (28.73) 0.614Overall change from baseline 6.0 (17.92) 19.7 (20.22)

FSH (IU/L) 0.606Baseline 4.6 (0.40) 4.4 (0.48)Overall change from baseline 0.2 (0.13) 0.1 (0.15)

LH (IU/L)Baseline 4.2 (0.37) 3.6 (0.44) 0.428Overall change from baseline 0.2 (0.26) 0.6 (0.29)

Prolactin (mg/L)Baseline 11.4 (1.05) 11.0 (1.24) 0.414Overall change from baseline 0.2 (0.78) 1.2 (0.88)

Adrenal axisCortisol (nmol/L)Baseline 369.1 (23.32) 388.1 (27.53) 0.354Overall change from baseline 24.6 (17.25) 0.2 (19.64)

ACTH (pmol/L)Baseline 10.4 (2.12) 5.1 (2.51) 0.871Overall change from baseline �1.3 (0.71) �1.1 (0.81)



groups (1 dysmenorrhea, 5 irregular menstruation,4 amenorrhea).

DISCUSSION

This study represents the first definitive assessment ofthe effects of ramelteon, a melatonin receptor agonist,on endocrine function in humans. While studies inanimals conclusively demonstrate the importance ofmelatonin and its receptors in regulating seasonalreproduction, the role of this system in humanendocrine function remains unclear. Previous studiesof exogenous melatonin administration in humans haveyielded conflicting results, probably due to small sizeand a wide variety of study designs and subjects. In astudy of ten healthy men (aged 21–33 years), 3mg ofmelatonin administered for 4 days resulted in a smallincrease in cortisol and prolactin, measured over 24 h(Kostoglou-Athanassiou et al., 1998). In another studyof six healthy men (aged 23–32 years), exogenousadministration of 2mg melatonin for 2 months hadno significant effect on T3, T4, TSH, or prolactinconcentrations (Terzolo et al., 1990). However, a study

of seven women showed that a single dose of melatonin4mg significantly increased the levels of prolactin(Terzolo et al., 1993). In a study comparing older(aged 50–62 years) and younger (aged 42–49 years)women, long-term melatonin 3mg treatment result-ed in significant increases in T3 concentrations atmonths 3 and 6 and a significant increase in T4concentrations at month 6 for both age groups(all p< 0.05) (Bellipanni et al., 2001). In youngerwomen only, 6 months of melatonin 3mg nightly led toa significant decrease in plasma LH (Bellipanni et al.,2001). A study of eight healthy men (mean age23.4 years) showed that 3 months of melatonin 3mgincreased estrogen levels in 2 of the men leading toreduced semen quality (Luboshitzky et al., 2002).Collectively, these studies do not provide a consensusregarding the endocrine effects of exogenous melato-nin and the role of melatonin receptors in humans.Previous clinical studies of ramelteon, a potent

and specific agonist of MT1 and MT2 receptors,have included assessments of endocrine function. In ashort-term (28-day) placebo-controlled assessment ofhealthy men and women (mean age 29.7 years),

Table 2. Summary of the overall changes from baseline for the thyroid, adrenal, and reproductive axes in women

Variable Placebo (n¼ 35) Ramelteon 16mg (n¼ 34) p-value (comparison with placebo)

Thyroid axisTSH (mU/L)Baseline 1.8 (0.15) 1.4 (0.15) 0.378Overall change from baseline 0.2 (0.09) 0.1 (0.10)

Free T4 (pmol/L)Baseline 12.7 (0.30) 12.3 (0.30) 0.541Overall change from baseline 0.0 (0.20) 0.2 (0.23)

Total T4 (nmol/L)Baseline 97.3 (3.32) 95.8 (3.33) 0.626Overall change from baseline �0.1 (1.74) �1.3 (1.95)

T3 (nmol/L)Baseline 1.4 (0.04) 1.5 (0.04) 0.966Overall change from baseline 0.0 (0.03) 0.0 (0.03)

Reproductive axisEstradiol (pmol/L)Baseline 262.0 (43.73) 287.2 (43.84) 0.299Overall change from baseline 32.6 (27.33) �8.5 (31.51)

FSH (IU/L)Baseline 6.1 (0.52) 5.2 (0.52) 0.209Overall change from baseline 1.4 (0.54) 0.5 (0.61)

LH (IU/L)Baseline 5.9 (0.98) 6.9 (0.99) 0.844Overall change from baseline 1.6 (0.96) 1.9 (1.10)

Prolactin (mg/L)Baseline 15.7 (1.20) 14.4 (1.20) 0.003Overall change from baseline �0.6 (1.19) 4.9 (1.32)

Adrenal axisCortisol (nmol/L)Baseline 398.7 (29.91) 376.0 (29.98) 0.325Overall change from baseline �10.6 (15.56) 11.3 (17.39)

ACTH (pmol/L)Baseline 7.3 (1.56) 4.2 (1.56) 0.219Overall change from baseline �1.7 (0.45) �0.9 (0.51)



ramelteon 16mg produced no significant change in anyof the hormones assessed (total T4, free T4, TSH, T3,estradiol [women only], FSH, LH, prolactin, freetestosterone [men only], total testosterone [men only],ACTH, or AM cortisol) (Tolbert et al., 2004). In a 1-year, open-label safety study of adults (aged 18–63years) and older adults (aged� 65 years), several of the

endocrine measures showed isolated and transientchanges from baseline (increased T4 at month 4[adults], decreased T3 at months 2 and 8 [older adults],increased free testosterone at months 1 and 2 [adults],decreased free testosterone at all Months [older adults],increased FSH at month 4 [both age groups], anddecreased cortisol at months 1 and 2 [both age groups]

Figure 1. Mean total triiodothyronine (T3) change from baseline at each time point. The baseline concentration (SE) of T3 for the placebo groupwas 1.4 nmol/L (0.03) and 1.5 nmol/L (0.03) for the ramelteon group. Follow-up data were collected 14 days after the last dose of study drug. There were no significantdifferences at any time point for any of the other thyroid indices (TSH, free T4, total T4). �p< 0.05

Table 3. Summary of menstrual diaries (Baseline, month 1, and month 6)

Menstrual data Placebo (mean 28.1 day cycle) Ramelteon 16mg (mean 27.8 day cycle)

Baseline (average before study drug)N 35 34Duration of menstrual flow (days) 4.6 4.7

Intensity of bleedingSlight, n (%) 6 (17.1) 2 (5.9)Moderate, n (%) 17 (48.6) 19 (55.9)Heavy, n (%) 9 (25.7) 8 (23.5)Heavy/Clots, n (%) 3 (8.6) 5 (14.7)

First mensesN 29 27Duration of menstrual flow (days) 5.4 5.3

Intensity of bleedingSlight, n (%) 7 (25.0) 4 (14.8)Moderate, n (%) 14 (50.0) 18 (66.7)Heavy, n (%) 4 (14.3) 3 (11.1)Heavy/Clots, n (%) 3 (10.7) 2 (7.4)Normal menses, n (%) 25 (86.2) 20 (74.1)

Sixth menses�

N 21 12Duration of menstrual flow (days) 5.7 4.8

Intensity of bleedingSlight, n (%) 4 (18.2) 1 (8.3)Moderate, n (%) 14 (63.6) 8 (66.7)Heavy, n (%) 2 (9.1) 3 (25.0)Heavy/Clots, n (%) 1 (4.5) 0 (0.0)Normal menses, n (%) 17 (77.3) 10 (83.3)

�1 subject in the placebo group did not report menstrual bleeding.



and at month 8 [adults]) (Richardson et al., 2006).However, the incidence of abnormal hormone levelswas low (<3% for each measure), and none of thechanges were considered clinically meaningful foreither age group (Richardson et al., 2006).The current 6-month, placebo-controlled trial offers

the most complete assessment of the long-termendocrine effects of ramelteon and, by extension,

melatonin receptor agonists. The isolated and transientchanges in thyroid function in this study were not feltto constitute a physiologically relevant alteration inthe thyroid axis. The overall increase in prolactinconcentration in women was also not consideredclinically meaningful since it was not associated with areduced probability of ovulation or menstrual irregu-larities. Further, the increase in prolactin concentration

Figure 3. Mean prolactin change from baseline at each time point in women. The baseline concentration (SE) of prolactin for the placebo group was 15.7mg/L(0.120) and 14.4mg/L (1.20) for the ramelteon group. Follow-up data were collected 14 days after the last dose of study drug. �p< 0.05

Figure 2. Mean free testosterone change from baseline at each time point. The baseline concentration (SE) of free testosterone for the placebo group was97.0 pg/mL (4.70) and 102.6 pg/mL (5.55) for the ramelteon group. Follow-up data were collected 14 days after the last dose of study drug. �p< 0.05



was transient, returning to baseline by 6 months inwomen who remained in the study. While prolactinchanges are a consistent feature of animal studies withmelatonin, previous studies in humans have providedinconsistent evidence for effects of melatonin. None-theless, the increase in prolactin in this study appearsto represent a reproducible effect. The mechanism ofsuch a prolactin change is unclear. Animal studiessuggest that this may reflect a direct action ofmelatonin receptor agonists on the prolactin releasingfactor (PRF) (Johnston, 2004). In humans, PRF doesnot appear to be the primary mediator of prolactinsecretion, and, consistent with this, changes in pro-lactin seen with ramelteon treatment were modest andtransient.There were several limitations to this study that may

have affected the results. This was an outpatient study,and therewas some variability in collection times of theAM blood sample. Since some of the hormonesevaluated in this study have endogenous circadianrhythms (Jordan et al., 1980; Sensi et al., 1993;Waldstreicher et al., 1996), it is possible that thevariability in sample collection times led to variabilityin hormone concentrations that may havemasked smalldrug effects. In addition, prolactin concentrationsfluctuate throughout the menstrual cycle in women(Vekemans et al., 1977), and samples may not havebeen collected at the same menstrual phase for everywoman. It should be noted that the current study wasperformed in subjects with chronic insomnia. Whilethe subjects in this study were screened for pre-existingendocrine pathology and there is no reason to believetheir endocrine function would differ from normalhealthy subjects, the generalizability of these findingsmay be limited. From a clinical perspective, peoplewith chronic insomnia are most likely to receive long-term treatment with ramelteon, and these data are mostrelevant to that population.The extent to which the effects of ramelteon

treatment can be extended to other melatonin receptoragonists may also be limited due to ramelteon’s uniquemechanism of action (specific for MT1/MT2 receptorswith no affinity for MT3 binding sites). While a rolefor MT3 in mediating endocrine effects has notbeen demonstrated, it remains possible that melatoninitself and other melatonin receptor agonists with lessspecificity may be associated with other distinctendocrine effects.

CONCLUSIONS

In human subjects, sustained exposure to ramelteon, apotent MT1/MT2 melatonin receptor agonist, produced

very limited endocrine effects in both men and women.The only consistent effect was a small increase inprolactin in women, and there was no evidence of anyreproductive consequences over the 6 months of drugexposure. These data support the conclusion thatmelatonin receptor activation plays only a small role inmodulating endocrine function in humans.

ACKNOWLEDGEMENTS

This study was supported by the Takeda PharmaceuticalCompany, Ltd. Sherry Wang-Weigand, MD, PhD is anemployee of Takeda Global Research and Develop-ment and participated in the study design, data analysisand interpretation, and writing of the manuscript. GaryRichardson, MD has acted as an investigator for previousstudies for Takeda Pharmaceuticals as well as other phar-maceutical companies. He fully participated in the studydesign, data analysis and interpretation, and writing ofthe manuscript. Assistance with writing and editing wasprovided by Sara Sarkey, PhD, an employee of TakedaPharmaceuticals North America. This trial has been regis-tered at clinicaltrials.gov: NCT00656994.

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Effects of long-term exposure to ramelteon, a melatonin receptor agonist, on endocrine function in adults with chronic insomnia