B12 Injection and Insomnia
It is highly unlikely that your 4pm B12 injection is causing your insomnia tonight. The evidence shows no association between B12 supplementation and insomnia, and in fact suggests B12 may have sleep-promoting effects rather than stimulating ones.
Why B12 Is Not Keeping You Awake
B12 does not act as a stimulant and has no established mechanism for causing acute insomnia. The American Academy of Sleep Medicine clinical practice guidelines for circadian rhythm disorders found very low quality evidence that oral B12 had no effect on sleep timing in adults with delayed sleep phase disorder 1. A multicenter study of 50 adults receiving 3mg daily oral B12 showed no clinically significant differences in sleep parameters compared to placebo 1.
Evidence Against B12 Causing Insomnia
Animal studies show sleep-promoting effects: Intravenous B12 administration in rats actually increased non-REM sleep duration, particularly during rest periods, rather than causing wakefulness 2
Human supplementation trials show no sleep disruption: A randomized controlled trial of 600 infants receiving daily B12 supplementation for one year found no effect on total sleep duration, nighttime sleep duration, or wake after sleep onset 3
B12 is indicated for your condition: The FDA label specifically lists small intestine bacterial overgrowth (SIBO) as an indication for B12 injection due to malabsorption 4, making your treatment medically appropriate
What May Actually Be Causing Your Insomnia
Your SIBO and malabsorption history suggest multiple potential contributors to sleep disturbance that are unrelated to the B12 injection:
Medical Conditions
- Gastrointestinal pathology and dysfunction directly disrupt sleep through discomfort, pain, and altered physiology 1, 5
- Patients with chronic medical conditions report significantly more sleep complaints as the number of conditions increases 5
Timing and Anxiety
- Anticipatory anxiety about sleep is a common perpetuating factor in insomnia 1
- The temporal association (injection at 4pm, insomnia that night) may create a false attribution that increases sleep-related worry
- Cognitive distortions about what caused poor sleep can perpetuate insomnia cycles 1
Other Medications
- Review all current medications, as β-blockers, diuretics, SSRIs, SNRIs, bronchodilators, corticosteroids, and decongestants commonly cause or exacerbate insomnia 1, 6, 5
- Over-the-counter preparations containing pseudoephedrine, phenylpropanolamine, or caffeine disrupt sleep 1
Clinical Caveats
One important nuance: Some older research suggested B12 might affect circadian rhythms by increasing light sensitivity and phase-advancing melatonin secretion 7, but this was with chronic oral dosing (3mg daily for 4 weeks), not acute injection. Even if this effect exists, it would theoretically help align your sleep-wake cycle rather than cause insomnia 7, 8.
The American Academy of Sleep Medicine explicitly states that B12 is "not indicated" for treating delayed sleep phase disorder in adults due to very low quality evidence 1, but this does not mean it causes insomnia—it simply means it doesn't effectively treat circadian rhythm disorders.
What to Do Instead
Focus on evidence-based insomnia management rather than attributing sleep problems to the B12 injection:
- Cognitive-behavioral therapy for insomnia (CBT-I) is the most effective treatment, with sustained effects up to 2 years in older adults 1
- Address sleep hygiene factors including caffeine intake, alcohol use, and environmental conditions 1
- Evaluate for primary sleep disorders if you experience true sleepiness (involuntary tendency to fall asleep), which would suggest obstructive sleep apnea, narcolepsy, or periodic limb movement disorder rather than insomnia 6, 5
- Continue your B12 treatment as prescribed for your SIBO-related malabsorption 4