31/01/2026
Frozen shoulder: why does the pain get worse at night?
Night pain is one of the most consistent and frustrating features of adhesive capsulitis, particularly during the early “freezing” phase. Many people describe daytime discomfort that becomes disproportionately severe once they lie down, often disturbing sleep and making side-lying intolerable. This isn’t random, and it isn’t just “because you’re not moving”. Several overlapping mechanisms explain why night-time pain is so common in frozen shoulder.
During the early stage of adhesive capsulitis, pain is the dominant symptom, often before any obvious restriction in movement appears. The joint capsule is inflamed and sensitised, and this sets the scene for nocturnal pain.
From a mechanical and positional perspective, lying down alters how load is distributed through the shoulder. When someone lies on the affected side, body weight compresses an already inflamed and thickened joint capsule. Even when lying on the opposite side or on the back, subtle changes in scapular position and reduced muscular support can increase capsular tension. In a joint where the capsule is irritable, these small positional changes can be enough to provoke pain.
There is also a clear circadian component. Inflammatory activity follows daily rhythms. Cortisol, which has anti-inflammatory effects, is lowest during the night. Lower nocturnal cortisol levels are associated with increased inflammatory signalling, which can amplify pain sensitivity in conditions driven by inflammation such as adhesive capsulitis. This helps explain why pain often feels deeper, sharper, or more constant at night compared with the daytime.
Pain perception itself changes at night. During the day, the nervous system is processing multiple competing sensory inputs and cognitive tasks. At night, when external stimuli reduce and attention shifts inward, pain signals become more salient. This doesn’t mean the pain is imagined; it means the brain is no longer “distracted” from the nociceptive input coming from the shoulder.
Where this gets particularly interesting is the role of melatonin. Melatonin levels rise naturally at night and are central to sleep regulation, but research over the past decade shows that melatonin is also involved in nociception in shoulder disorders. Studies examining frozen shoulder tissue have demonstrated increased expression of melatonin receptors MTNR1A and MTNR1B, along with acid-sensing ion channel 3 (ASIC3), a receptor involved in pain signalling. Inflammatory cytokines such as IL-1β and TNF-α appear to up-regulate these melatonin receptors. At physiological concentrations, melatonin has been shown to increase ASIC3 expression and IL-6 production, providing a plausible biological mechanism linking rising nocturnal melatonin levels with increased shoulder pain.
This creates an apparent paradox. On one hand, melatonin may contribute to nocturnal pain sensitisation in adhesive capsulitis through receptor-mediated pathways. On the other, experimental models suggest melatonin may also have anti-fibrotic and anti-inflammatory effects, with animal studies showing attenuation of capsular fibrosis and synovial hypertrophy. In other words, melatonin may be involved in both pain generation and longer-term modulation of the disease process, depending on context, timing, and tissue state.
Clinically, this explains why night pain is most severe during the freezing stage, why sleep disturbance is such a dominant complaint, and why patients often report that the shoulder feels far worse once they stop moving and lie down. It also explains why sleeping on the affected side is often intolerable and why simple reassurance that “it will settle” rarely helps in the early phase.
Management still centres on symptom control and maintaining tolerable movement. Pain relief strategies, corticosteroid injections when appropriate, and graded shoulder motion remain the mainstays. Practical advice around sleep positioning, such as avoiding pressure on the affected shoulder and supporting the arm to reduce capsular strain, can make a meaningful difference. The idea of targeting circadian biology, including melatonin pathways, is emerging, but at present remains an area of research rather than routine clinical practice.
Frozen shoulder night pain isn’t mysterious, psychological, or a sign that something dangerous is happening. It’s a predictable interaction between inflammation, joint mechanics, nervous system sensitisation, and circadian biology.
References
StatPearls. Adhesive Capsulitis (Frozen Shoulder). NCBI Bookshelf. Updated 2025.
Cho CH et al. Sleep quality and nocturnal pain in patients with shoulder disorders. J Shoulder Elbow Surg. 2015.
Rizk TE et al. Adhesive capsulitis of the shoulder: review of pathophysiology and current clinical treatments. Orthop Res Rev. 2017.
Xu Q et al. Melatonin plays a role as a mediator of nocturnal pain in patients with shoulder disorders. J Bone Joint Surg Am. 2014.
Lee HJ et al. Melatonin administration attenuates fibrosis progression in frozen shoulder syndrome: a rat model study. BMC Musculoskeletal Disorders. 2025.
AAFP. Adhesive Capsulitis: Diagnosis and Management. American Family Physician. 2019.
American Academy of Orthopaedic Surgeons. Frozen Shoulder (Adhesive Capsulitis). OrthoInfo.
